review session #2 motion and forces - passionately curious · 2018-05-08 · review session #2...
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Review Session #2Motion and ForcesMINNETONKA HIGH SCHOOL | IB PHYSICS
Reminder of our Equations
Units m m s-1 m s-1 m s-2 s
𝑣 = 𝑢 + 𝑎𝑡 𝑢 𝑣 𝑎 𝑡
𝑠 = 𝑢𝑡 + 12𝑎𝑡2 𝑠 𝑢 𝑎 𝑡
𝑣2 = 𝑢2 + 2𝑎𝑠 𝑠 𝑢 𝑣 𝑎
𝑠 = 𝑣+𝑢 𝑡2
𝑠 𝑢 𝑣 𝑡
Finding the Components of a Vector
20 N
θ = 34°
What are the x and y components of a 20 N force applied 34° from horizontal?
X-Component
Y-Component
Dropping a marble
𝑠
𝑢
𝑣
𝑎
𝑡
How fast must you launch a baseball straight in the air to reach the height of the Empire State Building (380 m)?*Assuming no air resistance*
Motion Graphs Guide
d
v
a
Co
nst
ant
Dis
pla
cem
ent
Co
nst
ant
+ V
elo
city
Co
nst
ant
-V
elo
city
+ A
ccel
erat
ion
Sp
eed
ing
up
+ A
ccel
erat
ion
Sl
ow
ing
Do
wn
-A
ccel
erat
ion
Sp
eed
ing
up
-A
ccel
erat
ion
Sl
ow
ing
Do
wn
Use the graphs to tell you MORE!Sl
op
eA
rea Un
der
Cu
rve
Displacement vs Time
Velocity vs Time
Acceleration vs Time
What Happens When…
v
t
a
d
t
What happens when you throw a ball straight up in the air?
Projectile Motion
X-Y Problem Solving Steps
X Y
𝑠
𝑢
𝑣
𝑎
𝑡
1. Start with Y and pretend it’s just a freefall problem
2. The air time is the same for X and Y so make tx = ty
3. Solve for X. • Constant velocity
• (ux = vx)• ax = 0• s = vt
Horizontal Projectile
X Y
𝑢
𝑣
𝑠
𝑎
𝑡
u
15 cm
1 m
Projectile at an Angle
24°
X Y
𝑢
𝑣
𝑠
𝑎
𝑡
vx =
vy =
You hit a baseball at 24° above the horizontal as a speed of 30 m/s. How far does the ball travel before it hits the ground?
Acceleration from FBD
How fast is this 100 kg block accelerating?
600 N
200 N
400 N100 N
Calculating Acceleration w/ Friction
Step 1:Find the Force from Friction• Fg = mg• R = Fg
• Ff = μ × R
Step 2:Find Fnet
• Fnet = Fpush - Ff
Step 3:Find acceleration
Fnet = ma a = Fnet / m
FpushFf
Fg
R
Calculate Friction | Try This…
Santa’s reindeer pull his 2000 kg sleigh with a force of 4980 N. How fast does the sleigh accelerate if the coefficient of kinetic friction (µk) is 0.05?
Air Resistance
Force of gravity is always constant
Force of air resistance increases whenvelocity increases
10
m/s
30
m/s
50
m/s
Fw
Fw
Fw
Terminal VelocityD
isp
lace
men
t (m
s-1
)
Time (s)
Vel
oci
ty (
m s
-1)
Time (s)
Ramp Problem
40°
m 10 kg
Fg
F⊥
F∥
R
Ff
Fnet
a
μ = 0.15
Calculating Gravitational Force
What is the force of gravity between the earth and the moon?
m = 6 × 1024 kgm = 7.4 × 1022 kg
r = 3.8 × 108 m
𝐹 = 𝐺𝑀𝑚
𝑟2G = 6.67 × 10-11 𝑁×𝑚2
𝑘𝑔2
Gravitation Field Strength
What is the gravitational field strength of the earth at the position of the moon?
m = 6 × 1024 kgm = 7.4 × 1022 kg
r = 3.8 × 108 m
𝑔 = 𝐺𝑀
𝑟2G = 6.67 × 10-11 𝑁×𝑚2
𝑘𝑔2
Defining Circular Motion | Summary
𝑣 =2𝜋𝑟
𝑇= 𝜔𝑟𝜔 =
2𝜋
𝑇
Angular Velocity Tangential Velocity (linear speed)
r radian
Centripetal Acceleration
A 3 kg rock swings in a circle of radius 5 m. If its constant speed is 8 m s-1, what is the centripetal acceleration?
What is the tension?
m = 2 kg
Fc
Fc
m 2 kg
vt 5 m/s
r 0.5 m
Fc
Fnet
Fg
FT
m 2 kg
vt 5 m/s
r 0.5 m
Fc
Fnet
Fg
FT
Top Bottom
Calculating Work
When you push a lawn mower, you are really applying a force down the angled handle bar as shown in this picture
FHow much work do you do when you push a lawn mower 20 m with a force of 200 N directed at an angle of 30° with the ground?
30°
Work and Power
How much power is required from the engine to move at a constant 30 m s-1? The force of drag (Ff) is 500 N. How much work is done in 4 seconds?
Conservation of Energy
100 m 70 m
What is the velocity of a 1 kg marble at point A?
Conservation of Energy | w/ spring
How far up the 15° incline of a pinball table will a 0.1 kg pinball move after it is launched? The spring constant is 100 N/m and is compressed by 0.08 m.
h
Work-Energy Theorem
A 0.005 kg bullet moving at 650 m/s hits a tree trunk and penetrates to a depth of 0.04 m. What is the force of the tree?
Which impulse is larger?Fo
rce
(N)
2
4
6
8
10
2 4 6 8 101 3 5 7 9
12
1
3
5
7
9
11
13
Time (s)
Calculating with Impulse-Momentum
You launch a marshmallow out of a 11 inch paper tube. If you can provide a consistent 0.28 N of force, how fast does the 0.7 g marshmallow travel when it exits the tube if it is in the tube for 0.05 seconds?
𝐹
𝑡
𝑚
𝑢
𝑣
Conservation of Momentum
mB
vBi = 0 m/s
mA
vAi = 4 m/smA = 18 kg mB = 12 kg
BEFORE
vBf = vf
mA
vAf = vf
mA = 18 kg mB = 12 kg
mB
After
What is the final velocity of block A and B if they stick together