Question 1

A baseball of mass $$0.15\ \mathrm{kg} is $$pitched at $$40\ \mathrm{m/s}. $$What is the magnitude of its momentum?

Accepted Answer

$$6.0\ \mathrm{kg\cdot m/s}$$

Question 2

Which of the following best describes the impulse-momentum theorem?

Accepted Answer

The impulse on an object is equal to the change in its momentum: $$\vec{J} = \Delta \vec{p}$$

Question 3

A person jumps from a height and lands with knees bent, taking $$0.5\ \mathrm{s} to $$come to rest. If the same person lands with legs straight and stops in $$0.1\ \mathrm{s}$$, how does the average force exerted by the ground compare in the two cases (assuming the same change in momentum)?

Accepted Answer

The average force is five times greater when landing with legs straight.

Question 4

Which of the following statements about elastic and inelastic collisions is correct?

Accepted Answer

In an elastic collision, both momentum and kinetic energy are conserved.

Question 5

Two ice skaters, initially at rest, push off from each other on frictionless ice. Which of the following is true about their momenta after they separate?

Accepted Answer

Their momenta are equal in magnitude and opposite in direction.

Question 6

A $$2\ \mathrm{kg}$$ object moving at $$5\ \mathrm{m/s}$$ collides elastically with a stationary $$3\ \mathrm{kg}$$ object. What is the velocity of the $$2\ \mathrm{kg}$$ object after the collision?

Accepted Answer

$$-1\ \mathrm{m/s}$$

Question 7

A $$1\ \mathrm{kg}$$ ball moving at $$4\ \mathrm{m/s}$$ collides head-on and sticks to a $$3\ \mathrm{kg}$$ ball at rest. What is their common velocity after the collision?

Accepted Answer

$$1\ \mathrm{m/s}$$

Question 8

Which of the following best describes the center of mass of a homogeneous sphere?

Accepted Answer

It is located at the geometric center of the sphere.

Question 9

A rocket ejects burned fuel at high speed in the opposite direction of its motion. According to the conservation of momentum, what happens to the rocket as it burns fuel?

Accepted Answer

The rocket gains forward momentum equal in magnitude and opposite in direction to the momentum of the ejected fuel.

Question 10

Which equation correctly gives the position vector of the center of mass for a system of particles?

Accepted Answer

$$\vec{r}_{\mathrm{cm}} = \frac{\sum m_i \vec{r}_i}{\sum m_i}$$

Question 11

A $$0.2\ \mathrm{kg}$$ ball moving at $$10\ \mathrm{m/s}$$ bounces elastically off a wall and rebounds with the same speed in the opposite direction. What is the magnitude of the impulse delivered to the ball by the wall?

Accepted Answer

$$4\ \mathrm{kg\cdot m/s}$$

Question 12

Which of the following is true about the motion of the center of mass of a system acted on by external forces?

Accepted Answer

It moves as if all the mass were concentrated at that point and all external forces acted there.

Question 13

A $$2\ \mathrm{kg}$$ cart moving at $$3\ \mathrm{m/s}$$ collides and sticks to a $$1\ \mathrm{kg}$$ cart at rest. What is the final velocity of the combined carts?

Accepted Answer

$$2\ \mathrm{m/s}$$

Question 14

Which of the following is a correct statement about momentum in a system with no external forces?

Accepted Answer

The total momentum of the system is conserved.

Question 15

A $$0.5\ \mathrm{kg}$$ ball is thrown at $$20\ \mathrm{m/s}$$ and comes to rest in $$0.1\ \mathrm{s}$$ after hitting a wall. What is the average force exerted by the wall on the ball?

Accepted Answer

$$100\ \mathrm{N}$$

Question 16

Which of the following best explains why cars are designed to crumple in a collision?

Accepted Answer

To increase the time over which the collision occurs, reducing the average force on passengers.

Question 17

In a one-dimensional elastic collision between two objects of equal mass, where one is initially at rest, what happens after the collision?

Accepted Answer

The moving object stops and the stationary object moves with the original velocity of the first.

Question 18

Which of the following is NOT a property of momentum?

Accepted Answer

Momentum is always a scalar quantity.

Question 19

A donut-shaped object has its center of mass:

Accepted Answer

Along the axis of symmetry, possibly outside the material of the object.

Momentum, Impulse, and Collisions – Study Notes

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