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PHY 231 HW5 Newton's third and first law View Basic/Answers

HW5 Newton's third and first law Begin Date: 2/10/2015 12:00:00 AM -- Due Date: 2/18/2015 11:59:00 PM End Date: 2/18/2015 11:59:00 PM

Problem 1:

Full solution not currently available at this time.

Given Newton’s First Law of Motion, what do we reasonably expect an object to do given the

following scenarios?

Variable Name Min Max Step Sample Value

Part (a) An object sits at rest with no unbalanced forces acting upon it. What do we expect this object to do?

Correct MultipleChoice: The object will remain at rest.

Choice Info:

The object will begin to move at a constant velocity.

Credit: 75

Feedback:

In order for an object to go from rest to any velocity, it

must experience an acceleration, which in turn means it

must have an unbalanced force acting upon it. The

statement indicates that the object does not have any

unbalanced force.

The object will begin to move at an accelerating

velocity .

Credit: 50

Feedback:

In order for an object to go from rest to any velocity, it

must experience an acceleration, which in turn means it

must have an unbalanced force acting upon it.

None of these answers.

Credit: 50

Feedback:

One of the answers is correct. If an object is at rest and

no unbalanced foreces are acting on it, how would it

begin to move in any way? What would cause the

motion?

Hints:

2 hints available

• What does the first part of Newton’s First Law of

Motion state? If this object is at rest and has no

unbalanced forces acting on it, then what would cause

it to move?

• An object at rest tends to stay at rest unless acted

upon by an unbalanced force.

Part (b) An object is traveling with a constant velocity with no unbalanced forces acting upon it. What do we expect

this object to do?

Correct MultipleChoice: The object will remain at the same speed, traveling in the same direction.

Choice Info:

The object will slow down and eventually come to

rest.

Credit: 90

Feedback:

If the object speeds up or slows down, it is experiencing

an acceleration, which means an unbalanced force is

acting upon it.

The object will speed up.

Credit: 75

Feedback:

If the object speeds up or slows down, it is experiencing

an acceleration, which means an unbalanced force is

acting upon it.

The object will begin to spin as it slows down.

Credit: 50

Feedback:

If the object begins to moving in a circle or slows down,

Hints:

1 hints available

• What does the second part of Newton’s First Law of

Motion state? If you have an object in motion with a

constant velocity and there are no forces, what would

cause it to change in any way?

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it is experiencing an acceleration, which means an

unbalanced force is acting upon it.

The object will remain at the same speed but change

direction.

Credit: 50

Feedback:

A change in direction, even with no change in speed, is

acceleration and thus only occurs when an unbalanced

force is acting on the object.


Credit: 25

Feedback:

One of the answers is correct. If you have an object in

motion with a constant velocity and there are no forces,

what would cause it to change in any way?

Part (c) An object sits at rest with an unbalanced force acting on it. What do we expect this object to do?

Correct MultipleChoice: The object will begin to move with an accelerating velocity.

Choice Info:

The object will remain at rest.

Credit: 50

Feedback:

An object at rest stays at rest unless acted upon by an

unbalanced force. This object is acted on by an

unbalanced force.

The object will begin to move with a constant

velocity.

Credit: 25

Feedback:

If the object has an unbalanced force, this would cause

the object to accelerate.


Credit: 25

Feedback:

One of the answers are correct. If a force is applied to

the object and nothing is in place to balance that force,

what would keep the object from moving? How would

the object remain stationary?

Hints:

3 hints available

• What does the first part of Newton’s First Law of

Motion state?

• An object at rest stays at rest unless acted upon by an

unbalanced force.

• This object is acted on by an unbalanced force.

Problem 2:



Problem 3:

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Problem 5:



Problem 6:

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Problem 8:



Problem 9:

Problem 10:



Problem 11:

Problem 12:



Problem 13:

Problem 14:

Full solution not currently available at this time.

A toy car is rolling down the ramp as shown in the figure. The car's

mass is m = 1.1 kg and the ramp makes an angle of θ = 11 degrees with

respect to the horizontal. Assume the car is rolling without friction.

Randomized Variables

m = 1.1 kg

θ = 11°

Variable Name Min Max Step Sample Value

m 1 2 0.1 1.1

t 10 20 1 11

Part (a) Using the coordinate system specified, give an expression for the acceleration of the car in terms of θ, g, and

the unit vectors i and j.

Correct Equation: a = g sin(θ) cos(θ) i - g sin(θ)2 j

Choice Info:

Valid Choices:

i, cos(θ), g, sin(θ), j, g, sin(θ), 2,

Partial Credit Choices with Feedback:

sin(θ) Credit: 75%

Feedback:You have a Trig. error. You should have cos(θ)

instead of sin(θ).

cos(θ) Credit: 75%

Feedback:You have a Trig. error. You should have sin(θ)

instead of cos(θ).

cos(θ) Credit: 75%

Feedback:You have a Trig. error. You should have sin(θ)

instead of cos(θ).

InValid Choices:

Hints:

2 hints available

• Draw the free body diagram, and write Newton's

second law for the x- and y-directions.

• There will be a component of the normal force in

both directions - so you can eliminate it to solve for

the accelearation.



cos(φ), sin(φ), cos(α), sin

(α), t, α, m, θ, d, β,

Part (b) What is the magnitude of this acceleration in m/s2?

Correct Algorithm: |a| = 9.81*sin(t*3.14159/180)

Choice Info:

|a| = 9.81*sin(11*3.14159/180)

|a| = 9.81*sin(11*3.14159/180)

|a| = 1.872

Buffer + or - 0.05616

Hints:

2 hints available

• Use your answer for part (a), and find the magnitude

of the acceleration.

• You might know this answer already if you have

seen this problem before with another coordinate

system.

Problem 15:

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