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Test Prep

# Test Prep

### Multiple Choice

#### 8.1Linear Momentum, Force, and Impulse

1.
What kind of quantity is momentum?
1. Scalar
2. Vector
2.

When does the net force on an object increase?

1. When Δp decreases
2. When Δt increases
3. When Δt decreases
3.

In the equation Δp = m(vfvi) , which quantity is considered to be constant?

1. Initial velocity
2. Final velocity
3. Mass
4. Momentum
4.
For how long should a force of $50N$ be applied to change the momentum of an object by $12kg⋅m/s$?
1. $0.24s$
2. $4.15s$
3. $62s$
4. $600s$

#### 8.2Conservation of Momentum

5.

In the equation L = Iω, what is I?

1. Linear momentum
2. Angular momentum
3. Torque
4. Moment of inertia
6.

Give an example of an isolated system.

1. A cyclist moving along a rough road
2. A figure skater gliding in a straight line on an ice rink
3. A baseball player hitting a home run
4. A man drawing water from a well

#### 8.3Elastic and Inelastic Collisions

7.

In which type of collision is kinetic energy conserved?

1. Elastic
2. Inelastic
8.

In physics, what are structureless particles that cannot rotate or spin called?

1. Elastic particles
2. Point masses
3. Rigid masses
9.

Two objects having equal masses and velocities collide with each other and come to a rest. What type of a collision is this and why?

1. Elastic collision, because internal kinetic energy is conserved
2. Inelastic collision, because internal kinetic energy is not conserved
3. Elastic collision, because internal kinetic energy is not conserved
4. Inelastic collision, because internal kinetic energy is conserved
10.
Two objects having equal masses and velocities collide with each other and come to a rest. Is momentum conserved in this case?
1. Yes
2. No

#### 8.1Linear Momentum, Force, and Impulse

11.

If an object’s velocity is constant, what is its momentum proportional to?

1. Its shape
2. Its mass
3. Its length
12.
If both mass and velocity of an object are constant, what can you tell about its impulse?
1. Its impulse would be constant.
2. Its impulse would be zero.
3. Its impulse would be increasing.
4. Its impulse would be decreasing.
13.
When the momentum of an object increases with respect to time, what is true of the net force acting on it?
1. It is zero, because the net force is equal to the rate of change of the momentum.
2. It is zero, because the net force is equal to the product of the momentum and the time interval.
3. It is nonzero, because the net force is equal to the rate of change of the momentum.
4. It is nonzero, because the net force is equal to the product of the momentum and the time interval.
14.

How can you express impulse in terms of mass and velocity when neither of those are constant?

1. $Δp=Δ(mv)Δp=Δ(mv)$
2. $ΔpΔt=Δ(mv)ΔtΔpΔt=Δ(mv)Δt$
3. $Δp=Δ(mv)Δp=Δ(mv)$
4. $ΔpΔt=1Δt·Δ(mv)ΔpΔt=1Δt·Δ(mv)$
15.

How can you express impulse in terms of mass and initial and final velocities?

16.

Why do we use average force while solving momentum problems? How is net force related to the momentum of the object?

1. Forces are usually constant over a period of time, and net force acting on the object is equal to the rate of change of the momentum.
2. Forces are usually not constant over a period of time, and net force acting on the object is equal to the product of the momentum and the time interval.
3. Forces are usually constant over a period of time, and net force acting on the object is equal to the product of the momentum and the time interval.
4. Forces are usually not constant over a period of time, and net force acting on the object is equal to the rate of change of the momentum.

#### 8.2Conservation of Momentum

17.

Under what condition(s) is the angular momentum of a system conserved?

1. When net torque is zero
2. When net torque is not zero
3. When moment of inertia is constant
4. When both moment of inertia and angular momentum are constant
18.
If the moment of inertia of an isolated system increases, what happens to its angular velocity?
1. It increases.
2. It decreases.
3. It stays constant.
4. It becomes zero.
19.
If both the moment of inertia and the angular velocity of a system increase, what must be true of the force acting on the system?
1. Force is zero.
2. Force is not zero.
3. Force is constant.
4. Force is decreasing.

#### 8.3Elastic and Inelastic Collisions

20.

Two objects collide with each other and come to a rest. How can you use the equation of conservation of momentum to describe this situation?

1. m1v1 + m2v2 = 0
2. m1v1m2v2 = 0
3. m1v1 + m2v2 = m1v1
4. m1v1 + m2v2 = m1v2
21.
What is the difference between momentum and impulse?
1. Momentum is the sum of mass and velocity. Impulse is the change in momentum.
2. Momentum is the sum of mass and velocity. Impulse is the rate of change in momentum.
3. Momentum is the product of mass and velocity. Impulse is the change in momentum.
4. Momentum is the product of mass and velocity. Impulse is the rate of change in momentum.
22.

What is the equation for conservation of momentum along the x-axis for 2D collisions in terms of mass and velocity, where one of the particles is initially at rest?

1. m1v1 = m1v1′cos⁡θ1
2. m1v1 = m1v1′cos⁡θ1 + m2v2′cos⁡θ2
3. m1v1 = m1v1′cos⁡θ1m2v2′cos⁡θ2
4. m1v1 = m1v1′sin⁡θ1 + m2v2′sin⁡θ2
23.

What is the equation for conservation of momentum along the y-axis for 2D collisions in terms of mass and velocity, where one of the particles is initially at rest?

1. 0 = m1v1′sin⁡θ1
2. 0 = m1v1′sin⁡θ1 + m2v2′sin⁡θ2
3. 0 = m1v1′sin⁡θ1m2v2′sin⁡θ2
4. 0 = m1v1′cos⁡θ1 + m2v2′cos⁡θ2

### Extended Response

#### 8.1Linear Momentum, Force, and Impulse

24.
Can a lighter object have more momentum than a heavier one? How?
1. No, because momentum is independent of the velocity of the object.
2. No, because momentum is independent of the mass of the object.
3. Yes, if the lighter object’s velocity is considerably high.
4. Yes, if the lighter object’s velocity is considerably low.
25.
Why does it hurt less when you fall on a softer surface?
1. The softer surface increases the duration of the magnitude, thereby reducing the effect of the force.
2. The softer surface decreases the duration of the impact, thereby reducing the effect of the force.
3. The softer surface increases the duration of the impact, thereby increasing the effect of the force.
4. The softer surface decreases the duration of the impact, thereby increasing the effect of the force.
26.

Can we use the equation $Fnet=ΔpΔtFnet=ΔpΔt$ when the mass is constant?

1. No, because the given equation is applicable for the variable mass only.
2. No, because the given equation is not applicable for the constant mass.
3. Yes, and the resultant equation is F = mv
4. Yes, and the resultant equation is F = ma

#### 8.2Conservation of Momentum

27.

Why does a figure skater spin faster if he pulls his arms and legs in?

1. Due to an increase in moment of inertia
2. Due to an increase in angular momentum
3. Due to conservation of linear momentum
4. Due to conservation of angular momentum

#### 8.3Elastic and Inelastic Collisions

28.
A driver sees another car approaching him from behind. He fears it is going to collide with his car. Should he speed up or slow down in order to reduce damage?
1. He should speed up.
2. He should slow down.
3. He should speed up and then slow down just before the collision.
4. He should slow down and then speed up just before the collision.
29.

What approach would you use to solve problems involving 2D collisions?

1. Break the momenta into components and then choose a coordinate system.
2. Choose a coordinate system and then break the momenta into components.
3. Find the total momenta in the x and y directions, and then equate them to solve for the unknown.
4. Find the sum of the momenta in the x and y directions, and then equate it to zero to solve for the unknown.