physics packet unit 3

Student Worksheets

Unit 3 - Dynamics and Forces

SCIENCE 8 – TYPES OF FORCES WORKSHEET

NAME:

Vocabulary

Action-at-a-distance Electrostatic Gravitational

Contact Force Magnetic

Elastic Friction Tension

Use your notes from pages 11 – 12 and the terms in the vocabulary box to fill in the blanks for the

following five questions. Each term may be used more than once.

1) A(n) is a push or a pull that acts on an object.

2) forces only have an effect on objects that they touch.

3) forces act on an object without

touching them.

4) works to slow down or stop motion due to surfaces

rubbing against each other. force is experienced by a

rope when it is pulled at either end. force is exerted when

a spring returns to its normal shape. These are examples of forces.

5) A(n) force pulls objects toward each other because they

have mass. A(n) force pulls or pushes on metals such as iron.

A(n) force causes pushing and pulling forces due to

differences in charge of the small particles that make up matter. These are examples of

forces.

6) Match each Descriptor on the left with the best Force on the right. You may use some forces more

than once.

Descriptor Force

An apple falls from a tree branch A. Elastic

A person uses a rope to pull a friend on a sled B. Tension

A magnet holds a picture on a fridge C. Friction

A person pulls a bow back and shoots the arrow D. Magnetic

A sock is stuck to a sweater as it comes out of the dryer E. Electrostatic

When a person stops pedalling, the bicycle slows down F. Gravitational

A meteor travelling through space moves faster and faster as it approaches Earth

A bungee cord pulls a jumper back up toward the platform from which he jumped

Your hands become warmer as you vigorously rub them together

When combing your hair, you notice hairs move outward from your head toward the comb

1

7) On the first blank line, state what type of force is illustrated in the picture (tension, friction, elastic,

gravitational, electrostatic, magnetic). On the second blank line, state whether it is a contact force or

an action-at-a-distance force.

Read the statements given below. If the statement is true, write “T” on the line in front of the statement.

If it is false, write “F” and rewrite the statement to make it true.

8) A force cannot set a motionless object in motion.

9) A force can make a moving object change direction.

10) A force can change the shape of an object.

11) Tension force slows down or stops motion due to surfaces rubbing against each other.

12) Elastic force pulls objects toward each other.

13) An example of magnetic force is lightning.

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©2009 Modeling Instruction Program 1 Free Particle Model, Ws1a v2.1

Free Particle Model Worksheet 1a:

Force Diagrams In each of the following situations, represent the object with a particle. Sketch all the forces acting upon the object, making the length of each vector represent the magnitude of the force. Also use congruency marks to indicate which vectors are equal in magnitude.

1. Draw a force diagram for the motionless cat on a rug. Label the forces and use equality marks on the force vectors.

2. Draw a force diagram for the skater, moving at constant speed across frictionless ice. Label the forces and use equality marks on the force vectors.

3. Draw a force diagram for the softball player who is slowing as she slides into the base. Label the forces and use equality marks on the force vectors.

Free Body Diagrams

Free Body Diagram

Free Body Diagram

Free Body Diagram

4

Free Body Diagrams

Free Body Diagram

Free Body Diagram

Free Body Diagram

4

Free Body Diagrams

Free Body Diagram

Free Body Diagram

Free Body Diagram

4

Free Body Diagrams

Free Body Diagram

Free Body Diagram

Free Body Diagram

4


4. Draw a force diagram for a chandelier that is suspended from the ceiling by a chain. Label the forces and use equality marks on the force vectors.

5. Draw a force diagram for the bucket of water that is being raised from the well at constant speed. Label the forces and use equality marks on the force vectors.

6. Draw a force diagram for a skydiver who has just left the plane and is still speeding up. Label the forces and use equality marks on the force vectors.

Free Body Diagram

Free Body Diagram

Free Body Diagram

5

Free Body Diagram

Free Body Diagram

Free Body Diagram

5

Free Body Diagram

Free Body Diagram

Free Body Diagram

5

Free Body Diagram

Free Body Diagram

Free Body Diagram

5


7. Draw a force diagram for a skydiver who is descending at a constant velocity. Label the forces

and use equality marks on the force vectors.

8. Draw a force diagram for a ball rising in a parabolic trajectory. Label the forces and use equality marks on the force vectors.

9. Draw a force diagram for a ball at the top of a parabolic trajectory. Label the forces and use equality marks on the force vectors.

Free Body Diagram

Free Body Diagram

Free Body Diagram

6

Ignore air resistance.

Consider air resistance.

Free Body Diagram

Free Body Diagram

Free Body Diagram

6



Free Body Diagram

Free Body Diagram

Free Body Diagram

6



Free Body Diagram

Free Body Diagram

Free Body Diagram

6



Net$Force$Worksheet!!!!!!!! !!!! !!!! !!!! !!!! !!!! !

The!force!that!results!from!all!the!combined!forces!acting!on!the!object!is!called!the!net$force.!Calculate!the!net!force!acting!on!the!box!in!the!following!problems.!!!Be!sure!to!include!the!direction!of!the!net!force!(left!or!right)!!

!"#$%&'''''''''''''''''''''''''&($)*+,%&&&-&&&&.&&&&/&&&&0&&&&1&&&&2&&&&3&

45$&6+)7$&85"8&)$9:;89&6)+#&";;&85$&7+#<*=$,&6+)7$9&"7>=?&+=&"=&+<@$78&*9&7";;$,&85$&!"#$%&'("A&B";7:;"8$&85$&=$8&6+)7$&"7>=?&+=&85$&<+C&*=&85$&6+;;+D*=?&E)+<;$#9A&&&F$&9:)$&8+&*=7;:,$&85$&,*)$7>+=&+6&85$&=$8&6+)7$&G;$H&+)&)*?58IJ&

0&!&

-A&

!$8&K+)7$%&&

.A&

!$8&K+)7$%&&

3&!& .&!&

0&!&

/A&

!$8&K+)7$%&&

0&!&

0A&

!$8&K+)7$%&&

2&!& /&!&

1A&

!$8&K+)7$%&&

L&!& 0&!&

2A&

!$8&K+)7$%&&

0&!& 1&!&

3A&

!$8&K+)7$%&&

/&!&/&!&

LA&

!$8&K+)7$%&&

0&!& 1&!&.&!&

MA&

!$8&K+)7$%&&

2&!&/&!&

-NA&

!$8&K+)7$%&&

0&!& 0&!&3&!&

For each problem below, use the information given in the picture to create a Free Body Diagram (FBD). Remember, in FBD’s forces are shown as ‘pulls’ not as ‘pushes’. After you draw the FBD, calculate the Net Force acting on the object.

Net Force Worksheet 1

7



7



7



7

11. What!is!net!force?

Show$your$work$on$problems$12914$12. A!boy!pulls!a!wagon!with!a!force!of!6!N!east!as!another!boy!pushes!it!with!a!force!of!4!Neast.!What!is!the!net!force?!

13. Mr.!Smith!and!his!wife!were!trying!to!move!their!new!chair.!Mr.!Smith!pulls!with!a!forceof!30!N!while!Mrs.!Smith!pushes!with!a!force!of!25!N!in!the!same!direction.!What!is!the!net!force?!

14. The!classes!are!playing!tug!of!war.!Mrs.!Larson’s!homeroom!pulls!with!a!force!of!50!N.Ms.!Mitko’s!homeroom!pulls!with!a!force!of!45!N!in!the!opposite!direction.!What!is!the!net!force?!And!who!won?!

15. What!is!a!balanced!force?

16. What!is!an!unbalanced!force?

17. Draw!a!picture!below!that!shows!an!example!of!a!balanced!force!(examples:!a!bird’snest!in!a!tree,!a!hat!on!a!person’s!head,!or!a!light!hanging!from!a!ceiling).!Show!the!forces!acting!on!the!object.!In!a!separate!picture!show!what!would!happen!to!the!object!if!the!forces!became!unbalanced.!

8888

1

Physics 2204 Unit 2: Dynamics

Worksheet 3: Net Force - One DimensionThe net force (Resultant force) is the vector sum of all the individual forces acting uponan object.

In other words, Fnet = F1 + F2 + F3 +..... F1, F2, and F3 represent the various forces acting upon an object. Like any force, the net force is avector and has a direction. Being the vector sum of all the forces, there may be some negativesigns present in the net force equation to indicate that one force is opposite in direction to anotherforce.Balance Forces (F

net

= 0) forces that combine to produce no net force. Acceleration of theobject is zero.

Unbalanced forces (Fnet

Ö0) - force that results when the net force acting on an object is notequal to 0 N. The object will accelerate1. 1. Look at the picture to the right. What is the net force on the car?Net force =_____________Is this force balanced or unbalanced? ________________________

2. Look at the picture to the right. The dog is pulling with a force of 30N to the rightand the boy is pulling backwards with a force of 18N. What is the net force on them?Net force =_________________Is this force balanced or unbalanced? ___________________

3. Look at the picture to the right. Both men are pushing on the refrigeratorwith a force of 100N. What is the Net force of on the refrigerator?Net force =_________________Is this force balanced or unbalanced? ___________________


∑F means Net Force∑F

9



9



9



9

2

2. Follow the checklist to complete the net force diagrams below.

1. Calculate the net force mathematically

2. Draw the net force arrow

3. Indicate if the forces are balanced or unbalanced

4. Indicate whether or not the object accelerates

(A)

1. Net force = ____________

2. Draw the net force arrow below.

3. The forces are:

a. balanced b. unbalanced

4. The object:

a. accelerates b . does not accelerate

(B)

1. Net force = ____________


3. The forces are:


4. The object:


(C)

1. Net force = ____________


3. The forces are:


4. The object:


(D)

1. Net force = ____________


3. The forces are:


4. The object:


(E)

1. Net force = ____________


3. The forces are:


4. The object:


(F)

1. Net force = ____________


3. The forces are:


4. The object:


10101010

Intro to Vectors!!! (Please do not write on this page)

Getting Started: Go to the following site: http://phet.colorado.edu/web-pages/simulations-base.html On the left side, scroll down to find “Math Tools” and click it. New icons appear on the right side of the screen. Scroll down on the right side until you see “Vector Addition” and click on the icon. The program may take a few minutes to load. Just like last time, play around with the program a bit to get comfortable with it. Questions: Before you begin these questions… under Component Display click the circle next to “Style 2” and Check the box next to “Show Grid”. These settings will not change for the rest of the activity. Answer all questions in complete sentences. 1. Drag a vector into the grid.

a. What does Rx represent? b. What does Ry represent? c. What does Θ represent? d. What does |R| represent?

2. Why does the vector have an arrowhead? What does that arrowhead indicate? 3. Reshape your first vector so that it is completely horizontal. Move that vector to (0,0).

What is the value of Rx? Ry? Θ? |R|? Do these values make sense? 4. Drag another vector into the grid. Reshape it so it is completely vertical. Move that vector

so that the tail of the arrow is touching the tip of the other vector on your screen. For this new vector, what is the value of Rx? Ry? Θ? |R|? Do these values make sense?

5. What have you begun to create? Draw what you see on the screen TO SCALE on your

own paper. 6. Click on the “Sum” button. A new vector appears on your screen. Drag it so that the tail of

the vector is at (0,0). What is the value of Rx? Ry? Θ? |R|? Do these values make sense?

7. Draw the new vector TO SCALE on the picture you drew for #5. How do you believe the

value for |R| was determined? Calculate it on your own to verify the computer’s result. SHOW ALL YOUR WORK!

8. Does the method you used work for all triangles? If not, what special types of triangles

does this method work for? 9. Drag all of your vectors to the trash. Create a new vector that starts at (0,0) and is not

completely horizontal or completely vertical. What are the values of Rx? Ry? Θ? |R|? Do these values make sense?

https://phet.colorado.edu/sims/vector-addition/vector-addition_en.html

Vector Addition Activity



11





11





11





11

10. What type of triangle is made? Draw what you see on the computer screen on your own page TO SCALE. Using the value of |R| and Ry, how would you calculate Rx? Verify the value of Rx by calculating it on your own. SHOW ALL YOUR WORK!

11. Create another vector that is not completely horizontal or completely vertical. Drag it so

that its tail is touching the tip of the vector from #9. What are the values of Rx? Ry? Θ? |R|? Do these values make sense?

12. Add the vector from #11 to your picture. Be sure to draw it TO SCALE on your paper.

Click the “Sum” button. Move the new vector so that its tail is at (0,0). Draw this vector to scale on the drawing you made in #9 and 11.

13. For your newest vector, what are the values of Rx? Ry? Θ? |R|? Do these values make

sense? 14. For your newest vector, how was Rx determined? How was Ry determined? How was |R|

determined? Try to verify the results the computer gave you by calculating the |R| yourself. SHOW ALL YOUR WORK!

15. In general, if you know the measurements of the horizontal parts (components) of vectors

and you know the measurements of the vertical components of vectors, how can you find their sum (resultant)?

12121212

Physics:AdditionofVectorsPractice1. Ans.(83.8mat15.7oNofE)2. (Ans.45kmat29oNofE)3. (Ans.29.3mat7.9oNofE)

A hiker walks 27.0 km from her base camp at 35o south of east. The next day, she walks 41.0 km in a direction 65o north of east. Find the magnitude and direction of her resultant displacement for the two days.

Find the resultant of the two vectors shown below:

75o35o

43m

112m

+/- +/-x-comp. (cos) y-comp. (sin)

1)

2)

R) < , >


35o25o

10m

23m

13131313

4. (Ans.23.9km/hat5oSofE)5.6.


40o

70o

23 km/h


1)

2)

R) < , >

18 km/h

14141414

Physics:AdditionofVectorsPractice21. Ans.(27.8kmat26oNofW)2. (Ans.43.5mat58oNofW)3. (Ans.49.3mat52oNofE)


40o

57o

49 km


1)

2)

R) < , >

23 km


1)

2)

R) < , >


45o

15o

85m

83m

Find the resultant of the vectors shown below:

75o35o

43m

104m

25o

48m

+/- +/-x-comp. (cos) y-comp. (sin)1)

2)

3)

R) < , >

1515

4. (Ans.9.4mat41oSofW)5. (Ans.730mat53oNofW)6. (Ans.203Nat83oSofW)

Find the resultant of the vectors shown below:

67o24o

12m

10m


2)

3)

R) < , >

8m

A student wandering in the woods leaves camp and walks 700m due North, turns and walks 200m at a direction 35o South of East, then turns to head 600m due West. What is the student's displacement from her original position?


2)

3)

R) < , >

A person pushes down on a box with a force of 55N at an angle of 55o S of E. A person on the other side of the box pushes down with a force of 80N at an angle of 45o S of W. The weight of the box is 100N. What is the resultant force on the box?


2)

3)

R) < , >

1616

StaticEquilibriumWorksheet11.Aforceof55Npushesdownwardatanangleof47otothehorizontalonanobjectrestingonthefloor.Theobjectdoesnotmove.IftheNormalforceactingupwardis131.2Nfindtheweightoftheobject.2.Aforceof19Npullsupwardatanangleof22otothehorizontalona60Nobjectrestingonthefloor.Theobjectdoesnotmove.FindtheNormalforceandtheFrictionforceactingontheobject.3.Anobjectonthefloorexperiencestwoseparateappliedforces.Thefirstisaforceof20Npushingdownwardfromtheleftatanangleof30otothehorizontal.Thesecondisaforceof30Npullingupwardtotherightatanangleof63o.IftheNormalforceupwardis193.3N,whatistheweightoftheobject?

17

(Ans. Fg = 91N Ffr = 38N)

(Ans. Fn = 52.9N)

(Ans. Fg = 210N)

17

(Ans. Fg = 91N Ffr = 38N)

(Ans. Fn = 52.9N)

(Ans. Fg = 210N)

4.Apersonweighing220Nissittingontopofatrunk.IfthefloorispushingupwithaNormalforceof360N,whatistheweightofthetrunk?(Ans.140N)5.A50Ndogissittingonachairthatweighs80N.Achildtriestopullthechairtotherightwithaforceof35N,butthechairdoesn'tmove.FindtheNormalforceandtheFrictionforceactingonthechair.(Ans.Fn=130N,Ffr=35N)6.Aboxofsnowglobesweighs60N.Apersonistryingtopulltheboxalongthefloorusingarope.Theypullwithaforceof40Nappliedatanangleof63oNorthofEast,buttheboxdoesn'tmove.FindtheNormalforceandtheFrictionforceactingonthebox.(Ans.Fn=24.4N,Ffr=18.2N)

1818

7.Ashoppingcartisfullofgroceries.Apersonpushesdownonthecartwithaforceof75Natanangleof40otothehorizontal.Ifthenormalforceoftheflooronthecartis73N,findtheweightofthecart.(Ans.25N)8.Twopeoplepushonaboxthatweighs50N.Onepersonpushesdowntotherightwithaforceof120Natanangleof37otothehorizontal.Theotherpersonpushesdowntotheleftwithaforceof54Natanangleof25otothehorizontal.Theboxdoesnotmove.FindtheNormalforceandtheFrictionforceactingonthebox.(Ans.Fn=145N,Ffr=47N)9.Twopeoplearetryingtolifta166Nboxofftheground.Thefirstpersonliftsuptotherightwithaforceof80Natanangleof40o.Thesecondpersonliftsuptotheleftwithaforceof90Natanangleof60o.Theboxdoesnotmove.FindtheNormalforceandtheFrictionforceactingonthebox.(Ans.Fn=37N,Ffr=16N)

1919

StaticEquilibriumWorksheet2(InclinedSurfaces)

1.Anobjectweighing110Nissittingmotionlessonaninclinedsurface.Thesurfacemakesa56oanglewith

theground.FindtheNormalforceandtheFrictionforceactingontheobject.

2.Acarweighing75,000Nissittingonahillwhichisinclined24otothehorizontal.FindtheNormalforceand

theFrictionforceactingonthecar.

3.Theanglebetweenaninclinedrampandthegroundis67o.A400Nobjectsitsmotionlessatthetopofthe

ramp.ConstructaFreeBodyDiagramtoshowthissituationanddeterminetheNormalandFrictionforces

actingontheobject.

Fg

FgFg

20202020

(Ans. Ffr = 91.2 N ; Fn = 61.5 N )

(Ans. Ffr = 30,505 N ; Fn = 68,516 N )

(Ans. Ffr = 368.2 N ; Fn = 156.3 N )

4.Amanissittingonahillthatisinclined35oabovethehorizontal.Ifthenormalforceofthegroundpushingupwardonthemanis153N,howmuchdoesthemanweigh?5.Aboxisrestingmotionlessonarampthatistilted20otothehorizontal.Ifthefrictionforceactingontheboxis217N,whatdoestheboxweigh?6.AU-Haultruckisparkedonaslanteddriveway.Thetruckweighs15,000N.TheNormalforcepushingupwardonthetruckis10,000N.Atwhatangleisthedrivewayslanted?

21212121

(Ans. 187 N )

(Ans. 634 N )

(Ans. 48.2∘ )

Newton’s First Law IPC

Name Period

Newton’s First Law Examine the forces acting on the freezer in the diagram and answer questions 1 – 3.

1. Are there any balanced forces acting on the freezer? If so, what are they?

2. Is there a net force acting on the freezer? If so, label it

on the diagram. Then, describe which forces interact and how they interact to produce the net force.

3. Describe the motion of the freezer. Will its velocity change? If yes, how?

4. Which object has more inertia – a bowling ball or a tennis ball? Explain.

5. How does inertia influence your ability to roll a bowling ball versus a tennis ball? Explain.

6. Write Newton’s First Law of Motion in your own words. You MAY NOT use the following words: at

rest, motion, constant velocity, net force.

7. Describe how Newton’s First Law applies to the following situations:

a. You slam on the brakes to stop your car suddenly.

b. You slam on the accelerator to get going quickly.

c. You make a sudden right turn.

d. You make a sudden left turn.

N Ffriction

W

Fappl

iied

22222222

Physics Name: ________________________ Date: ___________________

Weight and Newton’s 2nd Law 1. How much net force is needed to accelerate a 25 kg object at +3 m/s2?

Given:

Find:

2. A +50 N net force is applied to a 100 kg box. What is the acceleration of the box? Given:

Find:

3. A net force of +10 N is used to accelerate an object at +3.5 m/s2. What is the mass of the object? Given:

Find:

4. A 25 kg box is pushed by a -15 N net force. What is the acceleration of the box? Given:

Find:

5. A 10 kg object must be accelerated at +4 m/s2. What net force must be applied? Given:

Find:

6. An acceleration of +3.5 m/s2 results when two forces act on an object. The first force is 100 N to the right and the second force is 40 N to the right. (A) What is the net force on the object? (B) What is the object’s mass? Given:

Find:

23232323

(Ans. 75 N)

(Ans. .5 m/s²)

(Ans. 2.86 kg)

(Ans. -.6 m/s²)

(Ans. 40 N)

(Ans. a) 40 N right b) 400 kg)

7. Find the weight of a 1200 kg car. Given:

Find:

8. Find the weight of a 7 g tennis ball. Given:

Find:

9. What is the mass of a 650 N student? Given:

Find:

10. What is the mass of a 26 N crate? Given:

Find:

11. What is the mass of a 35,000 N truck? Given:

Find:

12. What is the weight of a 25 kg mass? Given:

Find:

24242424

(Ans. 11,760 N)

(Ans. .07 N)

(Ans. 66.3 kg)

(Ans. 2.65 kg)

(Ans. 3571 kg)

(Ans. 245 N)

PROBLEM SOLVING WITH NEWTON’S LAWS Name

1) The net force on a 5.0kg bowling ball is 20.0N. What is the acceleration of the bowling ball?

2) A baseball is hit by a bat, with a force of 1.0x103N, and accelerates at 4.0x103m/s2. What is the ball’s mass?

3) What net force is needed to accelerate a 3.0x104kg spacecraft at 2.5m/s2?

4) An 873kg dragster, starting from rest, attains a speed of 26.3m/s in 0.590s. A) What was the acceleration of the dragster?

B) What was the net force needed to accelerate the dragster?

C) Assume that the driver has a mass of 68.0kg. What horizontal force does the seat exert on him?

5) How much total force is needed to accelerate a 2.0kg block of wood at 4.0m/s2 along a rough table, against a force of friction of 10.N?

25252525

(Ans. 4 m/s²)

(Ans. .25 kg)

(Ans. 75,000 N)

(Ans. 44.6 m/s²)

(Ans. 38,936 N)

(Ans. 75,000 N)

(Ans. 3,033 N)

(Ans. 18 N)

6) A 0.50kg cart, initially at rest, accelerates at 3.0m/s2 over a distance of 10.m. A) What net force is acting on the cart?

B) How fast is the cart moving at the end of the track?

C) How long did it take the cart to travel the 10.m down the track?

7) A fully loaded Saturn V rocket has a mass of 2.92x106kg. It’s engines have a thrust upward of 3.34x107N.

a. What is the downward force, caused by gravity, on the rocket at blastoff?

b. What is the net force on the rocket at blastoff?

c. What is the acceleration of the rocket as it leaves the launch pad?

d. As the rocket travels upwards, the engine thrust remains constant, but the mass of the rocket decreases. Why?

e. Does the acceleration of the rocket increase, decrease, or remain the same as the engines continue to fire? Explain your answer using Newton’s laws.

26262626

(Ans. 18 N)

(Ans. 7.7 m/s)

(Ans. 2.6 s)

(Ans. 2.86 x 10⁷ N)

(Ans. 4,784,000 N)

(Ans. 1.64 m/s²)

(Ans. 1.5N)

8) A force of 36N gives a mass (m1) an acceleration of 4.0m/s2. The same force gives another mass (m2) an acceleration of 12m/s2. What acceleration will this same force give if m1and m2 are fastened together?

9) A man, with a mass of 1.0x102kg, slides across a frozen lake with an initial speed of 5.5m/s. Friction slows him, and after 4.3s he comes to a stop.

a. What was his acceleratiuon?

b. What was the net force, caused by friction, that caused him to stop?

c. How far did he slide across the lake?

10) Two toboggans are connected by a rope. The first toboggan has a mass of 60.kg and the second has a mass of 40.kg. The two toboggans are pulled by a rope connected to the front of the first toboggan. The force exerted by the rope is 250N. Ignore any friction forces here.

a. What is the acceleration of the two toboggans together?

b. What is the tension, force, in the rope connecting the toboggans?

27272727

IntroductiontoMeasuringFrictionActivityNamesofGroupMembers:_________________________________________________________Pd._____BackgroundInformation:

Frictionistheresistancefeltwhenonesurfaceslidesalonganothersurface.Forinstance,pushingawoodencratealongthestreetbringsawoodensurfaceintocontactwithacementsurface.Pushingthesamewoodencratealongicewould,ofcourse,bemucheasier.Theamountoffrictionbetweendifferenttypesofsurfacesvariesdependingonthespecificsurfacesyouaredealingwith.

Frictionalsodependsupontheforcewithwhichtwosurfacesarepressingtogether.Ifthecratementionedaboveisempty,therewillbelessfrictionthanifitwerefull.Itwouldn'tbepressingagainstthegroundasmuch.WeuseNormalForcetomeasurehowhardonesurfaceispressingagainstanother.Whenanobjectisonalevelsurfacewithnootherforcesactinguponit,theNormalForcewillbethesameastheweightoftheobject.Thisisthesituationwewillstudyinthisactivity.

ForeverysetoftwosurfacesthereexistsafactorcalledtheCoefficientofFriction(μ).Thisisanumberbetween0and1thatisusedtohelpuscalculatehowmuchfrictionforcetherewillbebetweentwosurfaces.CoefficientsofFrictionarespecifictothedifferentsurfacesinvolvedso,forexample,thereisonecoefficientoffrictionforglassslidingonwood,anotherforwoodslidingontile,anotherforrubberslidingoniron,etc.Inotherwords,coefficientsoffrictionarenotthingswememorize-theyarethingswecalculateorlookup.

TherearetwotypesofCoefficientsofFriction:StaticandKinetic.TheCoefficientofStaticFriction(μs)helpsusdeterminehowmuchforceittakestogetonesurfacetostarttoslidealonganothersurface.TheCoefficientofKineticFriction(μk)helpsusdeterminehowmuchforceittakestokeeponesurfaceslidingalonganotheroncetheyarealreadysliding.Inthisactivity,youaregoingtomakemeasurementsthatwillallowyoutocalculateCoefficientsofFrictionforseveralsurfaces.

Materials:NewtonScale,WoodBlocks(Plainwood,Glass,andSandpaper),Woodenplank,AdditionalmassesProcedure:

1)Beginwiththeplainwoodenblock.Measureitsmassusingtheelectronicscaleatthefrontoftheroom.RecordthismassintherowforTrial0inthetableontheothersideofthispaper.

2)Placetheblockonthewoodenplank.Havesomebodyinyourgroupholdtheplankinplacesoitdoesn'tslide.AttachthehookontheNewtonscaletotheeyehookontheblock.Begintopullverygraduallyattheblockuntilitjustbeginstoslide.Recordtheamountofforce,inNewtons,thatittakestobegintoslide.WritethisinthecolumnforMaxFs.Then,pulltheblockalongtheboardataconstantvelocityandrecordtheforcenecessarytokeepitsliding.(Thisforceshouldbeslightlylessthantheforcenecessarytobeginitsliding.)

3)Next,placeasinglemassontopoftheblock.Recordthetotalmass(blockplusmass)inthetable.Nowrepeatstep2),recordingthenewforcenecessarytobegintheblockslidingaswellastheforceneededtokeepitmovingataconstantvelocity.

4)Followthesameprocedurewithtwomasses,andthenthreemassesontheblock,recordingthenewforcenecessaryeachtimetobegintheblockslidingandtokeepitsliding.

5)Onceyouhavecompletedallthesemeasurementsfortheplainwoodenblock,beginbackatstep1)andrepeattheentireprocessfortheblockwithaglassbottom.Thendothesamefortheblockwiththesandpaperbottom.

6)Afterrecordingallyourdata,completetheremainingcolumnsinthetablestodeterminethecoefficientsoffriction. 28282828

1.Friction:WoodonWood

Trial# TotalMass(Block+masses) Fn(=mg)

Forcetobeginmoving

(MaxFs)

Fs/Fn(μs)

Forcetomoveatconst.vel.

(Fk)

Fk/Fn(μk)

1

2

3

2.Friction:GlassonWood


Forcetobeginmoving

(MaxFs)

Fs/Fn(μs)


(Fk)

Fk/Fn(μk)

1

2

3

3.Friction:SandpaperonWood


Forcetobeginmoving

(MaxFs)

Fs/Fn(μs)


(Fk)

Fk/Fn(μk)

1

2

3

29292929

Friction Force Worksheet 1. A student wants to slide a steel 15 kg mass across a steel table. What force must the student apply in order to start the box moving? µs = .74 and µk = .57 (Ans. 108.8 N) 2. What force must the student apply to keep the mass in question #1 moving at a constant velocity? µs = .74 and µk = .57 (Ans. 83.8 N ) 3. A wooden desk has a mass of 74 kg. What minimum force must be applied to the desk to start it moving across a wooden floor? µs = .42 and µk = .3 (Ans. 304.6 N) 4. Once the desk from question #3 above is in motion, what force must be used to keep it moving at a constant velocity? µs = .42 and µk = .3 ( Ans. 217.6 N )

30303030

5. A Chevy Blazer has a mass of 1850 kg. If the car is traveling at 15 m/s and the driver slams on the brakes, causing the vehicle to skid, how far would the car travel before it stops on dry asphalt? µs = 1.0 and µk = .8 ( Ans. 14.3 m ) 6. How far would the car from problem #5 travel if it were skidding to a stop on ice? µs = .2 and µk = .15 (Ans. 76.5 m) 7. A curling stone with a mass of 18 kg and initial velocity 9.45 m/s slides 38 m across a sheet of ice in 8.0 s before it stops because of friction. What is the coefficient of kinetic friction between the ice and the stone? (Note: you will need to calculate the acceleration of the stone first.) (Ans. 0.12 )

31313131

AppliedStaticandKineticFriction1.A25kgblockisinitiallyatrestonarough,horizontalsurface.Ahorizontalforceof75Nisrequiredto

settheblockinmotion,anda60Nforceisrequiredtokeepitinmotionataconstantspeedonceitis

moving.Whatarethecoefficientsofstaticandkineticfriction?

2.Thecoefficientofstaticfrictionbetweena10kgobjectandtheflooris0.50.Whatisthemaximum

forcethatcanbeappliedontheobjectbeforeitstartsmoving?

3.A100kgobjectmovingat20m/scomestoastopoveradistanceof40m.Whatisthecoefficientof

kineticfrictionbetweentheobjectandtheground?

4.Ahockeypuckishitonafrozenlakeandstartsmovingwithavelocityof12.0m/s.5.0secondslater,

thevelocityofthepuckis6.0m/s.Whatisthecoefficientoffrictionbetweenthepuckandtheice?

5.A100kgobjectisatrestonahorizontalsurface.Thecoefficientofstaticfrictionbetweentheobject

andthesurfaceis0.60,whilethecoefficientofkineticfrictionbetweentheobjectandthesurfaceis

0.45.

a) Ifaforceof400Nisappliedfor5.0seconds,whatwillbetheforceoffrictionactingonthe

object?

b) Ifaforceof650Nisappliedfor5.0seconds,whatwillbetheforceoffrictionactingonthe

object?

c) Howmuchappliedforceisrequiredfortheobjecttostartmoving?

6.Provideonesituationwhereyouwouldwanttohavealowcoefficientofstaticfrictionandone

situationwhereyouwouldwanttohaveahighcoefficientofstaticfriction.

7.Provideonesituationwhereyouwouldwanttohavealowcoefficientofkineticfrictionandone

situationwhereyouwouldwanttohaveahighcoefficientofkineticfriction.

3232

Ans. Coeff. of Static = .30 Coeff. of Kin. = .24

Ans. 49 N

Ans. Coeff. of Kin. = .51

Ans. .12

Ans. 400 N , not enough to make the object start to move.

Ans. 441 N , the object will be moving, so kinetic friction applies.

Ans. 588 N

3232

Ans. Coeff. of Static = .30 Coeff. of Kin. = .24

Ans. 49 N

Ans. Coeff. of Kin. = .51

Ans. .12

Ans. 400 N , not enough to make the object start to move.

Ans. 441 N , the object will be moving, so kinetic friction applies.

Ans. 588 N

1

Net force and Coefficient of Friction Worksheet 1. Suppose a 10 N force is applied to the side of a 4.0 kg block that is sitting on a table. The block experiences a frictional force against the force that is applied.

a) Draw a free body diagram for the block? b) What is the weight of the block (FG)? c) What is the normal force on the block (FN)? d) If the coefficient of kinetic friction is µk = .20, what is the frictional force on the block (Fk)? e) What is the net force on the block? f) What is the acceleration of the block from the net force? g) What would be the minimum value of the coefficient of static friction in order for the block to remain

motionless? 2. A block weighing 300 N is moved at a constant speed over a horizontal surface by a force of 50 N applied parallel to the surface. What does the “constant speed” tell you about the forces acting on the block?

a) Draw a free body diagram for the block. b) What is the coefficient of kinetic friction (µk)? c) What is the mass of the block? d) What would be the acceleration of the block if µk = 0?

3. A hockey puck has a coefficient of kinetic friction of µk = .60. If the puck feels a normal force (FN) of 10 N, what is the frictional force that acts on the puck? What is the mass of the puck?

4. A large box is being dragged across the floor at constant velocity. If the box has a mass of 60 kg and it takes a 50 N force, acting horizontally, to drag the box, what is the coefficient of friction?

5. A bolder of mass 45 kg is pushed on a surface with a coefficient of kinetic friction of 0.85. What force has to be applied to produce an acceleration of 2 m/s2?

33333333

34343434

Newton’sThirdLaw Name 1. Ifyourweightistheforcecreatedbygravityonyourbody,whatisthereactionforce?2. IfyoujumpoffofaledgeandacceleratetowardtheEarth,theEarthwillacceleratetowardyouatthe sametimeduetoNewton’sThirdLaw.Whydon’tweseetheEarthmoveinthissituation?3. Thereisnothinginouterspaceforrocketexhaustgassestopushagainst.Howthencanarocket accelerateinouterspace?(Andyes,wedoknowthattheycanaccelerateinouterspace,thisisnot atrickquestion!)4. AfriendisarguingNewton’sThirdLawwithyou.Hestatesthatwhenabulletfiresfromagunthere mustbeanequalandoppositeforcebackwardonthebullet,andthattheseforceswouldcanceleach otherout.Therefore,hesays,thereisnowayabulletwouldbeabletomove,andthismeansNewton’s ThirdLawdoesn’twork.Howwouldyoubeabletoenlightenyourconfusedfriend?

3535

5. Nomatterhowhardahorsepullsonacart,thecartmustpullbackwithexactlythesameforceaccording

toNewton’sThirdLaw.Howcanacartpullahorse?(Forthisquestionassumethatthehorseandcart

areonlevelground.)

6. Abugsplattersonafast-movingcar’swindshield.Howdoestheforcefeltbythebugcomparetothe

forcefeltbythecar’swindshield?Explain.

3636

StaticEquilibriumReviewSheet1.Theanglebetweenaninclinedrampandthegroundis42o.A559Nobjectsitsmotionlessatthetopoftheramp.ConstructaFreeBodyDiagramtoshowthissituationanddeterminetheNormalandFrictionforcesactingontheobject.(Ans.Fn=415N,Ffr=374N)2.Aboxisrestingmotionlessonarampthatistilted60otothehorizontal.Ifthefrictionforceactingontheboxis392N,whatdoestheboxweigh?(Ans.Fg=453N)3.Aforceof90Npushesdownwardatanangleof32otothehorizontalonanobjectrestingonthefloor.Theobjectdoesnotmove.IftheNormalforceactingupwardis200Nfindtheweightoftheobject.(Ans.152N)

3737

GeneralandHonorsPhysics:Unit3TestReviewSheet

1.Askydiverisfallingthroughtheairwithaparachutetravelingataconstantvelocity.DrawtheFreeBodyDiagram.

2.Apersonpushesaboxacrossaroughfloorsothatitacceleratestotheright.DrawtheFreeBodyDiagram.

3.Abulletisshothorizontally.DrawitsFreeBodyDiagramafteritleavesthegun.Considerairresistance.

4.Threeforcesactonanobjectasshownbelow.Whatmustbethemagnitudeanddirectionoftheunknownforceinorderfortheobjectnottomove?(Ans.29.2Nat38oSofW)

5.Combinethegivenforcesandfindtheirresultantmagnitudeanddirection.(Ans.a)83Nat33oSofEb)70Nat60oNofE)a) b)6.Aboxweighing300Nrestsonthefloor.Aboywhoweighs80Nsitsontopofthebox,whilehisbrotherpullsuptotherightwithaforceof90Natanangleof65o.Theboxdoesnotmove.FindtheFrictionforceandtheNormalforceactingonthebox.(Ans.Ff=38N,Fn=298.4N)

7.Judithissittingontopofa150Ntrunkonthefloor.Hertwobrothersaretryingtomovethetrunk.Onebrotherpushesdownfromtherightatanangleof35owithaforceof50N,theotherpullsupfromtheleftatanangleof60owithaforceof35N.Ifthetrunkdoesn'tmoveandthenormalforceis230N,findJudith'sweightandthefrictionforce.(Ans.Fbw=81.7N,Ff=58.5N)

8.Twoforcesactona500Nboxthatisonthefloor.A58Nforceactsupwardtotherightatanangleof62o.A39Nforceactsupwardtotheleftatanangleof41o.Iftheboxdoesn'tmove,findtheNormalforceandthefrictionforceonthebox.(Ans.Ff=2.2N,Fn=423N)

9.a)FindtheNormalforceontheboxinthispicture.(Ans.50N)b)Findtheweightoftheobjectbelow.(Ans.270N)

10.Howmuchforcewouldittaketocausea55kgobjecttoaccelerateatarateof5m/s2?(Ans.275N)

53o

145N

43o

63N

23N

18N

?

41o80o

52 N

27 N

Fg = 65N

40o

Fg=?

Fn = 250N

22o

3838

Fjw

11.Assumingnofriction,whatconstantforcemustbeappliedtoa15,000Ncartomakeitaccelerateuniformlyfrom0m/sto37m/soveradistanceof75m?(Ans.13,969N)12.Aforceof67Nisappliedtoa98Nbooktoslideitacrossatable.Thebookacceleratesatarateof6m/s2totheright.Whatistheforceoffrictionbetweenthebookandthetable?(Ans.7N)

13.Aboxislyingonthefloor.Twopeoplepushonthebox.Onepersonpushesdownfromtheleftwithaforceof60Natanangleof60o.Another,shorterperson,pushesdownfromtheleftwithaforceof30Nfromanangleof30o.Ifthebox'smassis250kgandthereisnegligiblefrictionwiththefloor,atwhatratewilltheboxaccelerate?(Ans..22m/s2)

14.Asledisbeingdraggedalonginthesnowataconstantvelocitybyarope.Theropemakesa31oanglewiththehorizontalandexertsa48Nforce.Whatisthefrictionbetweenthesledandthesnow?(Ans.41N)

15.Astudentnoticesthatittakesabout250Nofforcetogetawoodendressertostartmovingacrossatilefloor,butonly100Ntokeepitmovingataconstantvelocity.Ifthedresserhasamassof212kg,whatarethecoefficientsofStaticandKineticFrictionforwoodontile?(Ans.µs=.12,µk=.048)

16.A500Nboxslidingacrossawarehousefloorat4m/sskidstoastopoveradistanceof75m.Whatisthecoefficientofkineticfrictionbetweentheboxandthefloor?(Ans.µk=.01)

HONORSONLY:17.Findtheresultantfortheforcesbelow:(Ans.243Nat6.3oSofE)18.A98Nobjecthangsfromtheceilingbytwocables.Thefirstcablemakesanangleof30owiththeceilingandthesecondmakesanangleof45o.Findthetensionineachcable.(Ans.71.7Nand87.9N)19.Anobjecthangsfromtheceilingbytwocables.Eachcablemakesanangleof65owiththeceilingandexertsatensionforceof90Nontheobject.Findtheweightoftheobject.(Ans.163N) 20.Youareinyourcar,mass2500kg,travelingdownthehighwaywithaspeedof15m/s.Youseetrafficaheadandapplythebrakes.Youslowdownto5m/sin2seconds.Whatwasthenetforceonthecar?(Ans.12,500N)21.Atruckhasamassof3850kg.Ifitistravelingat8m/sandthedriverslamsonthebrakes,causingthevehicletoskid,howfarwouldthecartravelbeforeitstopsondryasphalt?µs=1.0andµk=.8(Ans.4.1m)22.Ifthehangingmassis350grams,andthemassesareacceleratingat2.5m/s2,whatisthemassofthecart?Assumeafrictionforceof1Nbetweenthecarandthetable.(Ans.m1=.62kg)

112N

148N34N

63o

73o

3939

SUPPLEMENTAL MATERIALS

(ADDITIONAL PRACTICE)




ABRHS PHYSICS NAME: ______________________

Force Problems I

1. 1500 N 2. 3 m/s2 3. 50 kg 4. 2 m/s2 5. 250 N 6. 10,500 N 7. –3750 N 8. 244 N 9. 188 N

1. A car of mass 1000 kg is accelerating with a constant rate of 1.5 m/s2. What is the net force acting on the car?

2. An airplane is accelerating down the runway. The mass of the airplane is 15,000 kg. If the

engines are producing a net thrust of 45,000 N, what is the acceleration of the airplane? 3. There is a net force of 200 N acting on a girl on a skateboard. If her acceleration is 4 m/s2, what

is her mass? 4. Tony is pulling Fred, who is sitting in a wagon. Tony is pulling with a force of 250 N. Fred and

the wagon have a combined mass of 75 kg. If there is also a frictional force of magnitude 100 N acting on Fred, what is Fred's acceleration?

5. Sasha is pushing Kara with a force 350 N. Kara has a mass of 50 kg. If Kara is accelerating

with a rate of 2 m/s2, what is the magnitude of the force of friction acting on Kara? 6. A car of mass 1500 kg is accelerating with a rate of 3 m/s2. If the magnitude of the force of

friction is 6000 N, how much force must the engine be producing? 7. You are in your car, mass 1500 kg, traveling down the highway with a speed of 25 m/s. You see

traffic ahead and apply the brakes. You slow down to 15 m/s in 4 seconds. What was the net force on the car?

8. A happy physics student wants to determine how much force she can produce. Starting from

rest, she accelerates and covers 5 meters in only 1.5 seconds. If she has a mass of 55 kg, what was the net force on her?

9. A skateboarder, mass 75 kg, coasts from 15 m/s to 10 m/s over a distance of 25 meters. What

was the magnitude of the force of friction acting on the skateboarder?

4141

NEWTON’SLAWS Name 1. Howmuchnetforceisneededtoacceleratea15kgmassat2.8m/s2?2. Delon’scarisdead.Heispushingittotheeastoutoftheparkinglotwithaforceof250N.carter,beinga

goodfriend,comestohelpandalsopusheseastwithaforceof75N.IfDelon’scarhasamassof750kg,whatisthecar’sacceleration?

3. Hunterispullingonhislittleredwagontothewestwithaforceof125N.Lukedoesn’twanthimtotake

thewagonsoheispullingintheoppositedirectionwithaforceof75N.Ifthewagonhasamassof15kg,whatisthewagon’sacceleration?

4. Aplanesengineispushingitnorthwithaforceof1250N.Thewindisblowingtotheeastwithaforceof

125N.Iftheplaneisa775kgmass,whatisthemagnitudeofitsacceleration?

44

Unit3-DynamicsandNewton'sLaws-GroupProjectProblems1.Apersonistryingtopulla250Nboxalongthefloorusingarope.Theyfindtheymustpullwithaforceof100Nappliedatanangleof63oNorthofEastjusttogettheboxtostarttoslide.Findthecoefficientofstaticfrictionbetweentheboxandthefloor.(Ans..28)2.Twopeoplearetryingtolifta350Nboxofftheground.Thefirstpersonliftsuptotherightwithaforceof90Natanangleof45o.Thesecondpersonliftsuptotheleftwithaforceof70Natanangleof50o.Theboxdoesnotmove.FindtheNormalforceandtheFrictionforceactingonthebox.(Ans.Fn=232.8N,Ffr=18.6N)3.A400kgobjectissittingatrestatthetopofahillthatis30mhigh,and80mlong,measuredalongthehill.Ifthereisnofriction,howfastwilltheobjectbegoingatthebottomofthehill?(Ans.38m/s)4.Atruckisparkedonaslanteddriveway.Thetruckweighs18,000N.TheNormalforcepushingupwardonthetruckis10,000N.Atwhatangleisthedrivewayslanted?(Ans.56.3o)5.Youareinyourcar,mass2000kg,travelingdownthehighwaywithaspeedof30m/s.Youseetrafficaheadandapplythebrakes.Youslowdownto15m/sin5seconds.Whatwasthenetforceonthecar?(Ans.6000N)6.A20kgboxisbeingpulledataconstantvelocityonflatgroundbyaforceFatanangleof30oabovethehorizontal.Ifthecoefficientoffrictionbetweentheboxandthefloorisμk=0.33,findF.(Ans.62.5N)7.(H)Anobjectweighing82.2Nissuspendedfromtwostringsattachedtotheceiling.Thefirststringmakesanangleof20owiththeceilingandthesecondmakesanangleof55o.FindtheTensionsinthetwostrings.(Ans.48.8Nand80N)8.(H)Inthegivenfigure,m1=1.3kgandm2=4kg.Whenm2isreleased,m1acceleratesatarateof2.1m/s2.Findthefrictionforcebetweenm1andthetable.(Ans.2N)

(Ans. 24.3 m/s)

(Ans. 27.9 N)

StaticEquilibriumPracticeSheet

Foreachproblem,drawaFreeBodyDiagramandshowyourequationstofindthemissingforces.GENERAL&HONORS

1.Apersonweighing550Nissittingonachair.IfthefloorispushingupwithaNormalforceof780N,whatistheweightofthechair?(Ans.230N)2.Twopeoplearetryingtolifta1325Ntrunkofftheground.Thefirstpersonliftswithaforceof120Nat35oNorthofWest.Thesecondpersonliftswithaforceof150Nat42oNorthofEast.Thetrunkdoesnotmove.FindtheNormalforceandtheFrictionforceactingonthetrunk.(Ans.Fn=1155.8N,Ff=13.2N)3.A240Ncatissittingonastoolthatweighs100N.Awomantriestopullthestooltotherightwithaforceof50Natanangleof20oNorthofEast,butthestooldoesn'tmove.FindtheNormalforceandtheFrictionforceactingonthestool.(Ans.Fn=323N,Ff=47N)4.Aforceof76Npullsupwardatanangleof37otothehorizontalona300Nobjectrestingonthefloor.Theobjectdoesnotmove.FindtheNormalforceandtheFrictionforceactingontheobject.(Ans.Fn=254.3N,Ff=60.7N)

5.Aforceof30Npushesdownwardatanangleof70otothehorizontalonanobjectrestingonthefloor.The

objectdoesnotmove.IftheNormalforceactingupwardis200Nfindtheweightoftheobject.(Ans.171.8N)

6.Antableexperiencestwoseparateappliedforces.Thefirstisaforceof35Nat45oSouthofEast.Thesecond

isaforceof20Nat60oSouthofWest.IftheNormalforceupwardis560N,whatistheweightoftheobject

andtheforceoffriction?(Ans.Fg=518N,Ff=14.7N)

HONORSONLY:

7.Anobjecthangsfromtheceilingbytwocables.Eachcablemakesanangleof25owiththeceilingandexerts

aTensionforceof50Nontheobject.Findtheweightoftheobject.(Ans.42.2N)

8.A300Nobjecthangsmotionlessfromtheceilingbytwocables.Cable1makesanangleof35owiththe

ceiling.Cable2makesanangleof23owiththeceiling.Findthetensionforceineachcable.

(Ans.T1=323N,T2=294N)

physics packet unit 3

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