Question 1

A 60-kg archer stands at rest on frictionless ice and fires a 0.030-kg arrow horizontally at 85 m/s. What is the velocity of the archer immediately after firing the arrow?

Accepted Answer

$$-0.043\ \mathrm{m/s}$$

Question 2

Which of the following statements about linear momentum is correct?

Accepted Answer

Linear momentum is defined as $$\vec{p} = m\vec{v}$$ and is a vector quantity.

Question 3

A 2.5-kg stone is released from rest and falls toward Earth. After 4.0 s, what is the magnitude of its momentum? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$98\ \mathrm{kg} \cdot \mathrm{m/s}$$

Question 4

Two objects have equal kinetic energies. Which of the following is true about the magnitudes of their momenta?

Accepted Answer

Not enough information to tell

Question 5

Rank the following objects in order of the magnitude of their momentum, from largest to smallest:
A. Mass = 2.0 kg, kinetic energy = 2.0 J
B. Mass = 1.0 kg, kinetic energy = 2.0 J
C. Mass = 2.0 kg, kinetic energy = 4.0 J
D. Mass = 4.0 kg, kinetic energy = 4.0 J

Accepted Answer

D, C, A, B

Question 6

Which of the following best describes the law of conservation of linear momentum for an isolated system?

Accepted Answer

The total momentum of the system remains constant if the net external force is zero.

Question 7

A child in a boat throws a 6.40-kg package out horizontally at a speed of 10.0 m/s. The mass of the child is 26.0 kg and the boat is 45.0 kg. What is the velocity of the boat and child immediately after the throw? (Assume the system was initially at rest and ignore water resistance.)

Accepted Answer

$$-0.90\ \mathrm{m/s}$$

Question 8

Which of the following is true for a perfectly inelastic collision?

Accepted Answer

The objects stick together and move with a common final velocity.

Question 9

During a head-on collision between a 95.0-kg running back moving at $$3.75\ \mathrm{m/s}$$ and a 111-kg linebacker moving at $$-4.10\ \mathrm{m/s}$$, the two players stick together. What is their velocity immediately after the collision?

Accepted Answer

$$-0.48\ \mathrm{m/s}$$

Question 10

Which of the following best distinguishes an elastic collision from an inelastic collision?

Accepted Answer

In an elastic collision, both kinetic energy and momentum are conserved; in an inelastic collision, only momentum is conserved.

Question 11

A 1,500-kg car traveling east at $$25.0\ \mathrm{m/s}$$ collides at an intersection with a 2,500-kg truck traveling north at $$20.0\ \mathrm{m/s}. If $$the vehicles stick together after the collision, what is the magnitude of their velocity just after the collision?

Accepted Answer

$$15.6\ \mathrm{m/s}$$

Question 12

Which of the following is NOT a necessary condition for the conservation of linear momentum in a system?

Accepted Answer

The system must consist of at least two objects.

Question 13

A 160-g hockey puck strikes a 6.4-kg chest at rest on frictionless ice and embeds itself. The chest moves off at $$1.2\ \mathrm{m/s}. $$What was the puck’s speed before the collision?

Accepted Answer

$$49\ \mathrm{m/s}$$

Question 14

Which of the following real-world scenarios is best modeled as a perfectly inelastic collision?

Accepted Answer

A bullet embedding itself in a block of wood.

Question 15

Which equation correctly relates the net force to the time rate of change of momentum?

Accepted Answer

$$\sum \vec{F} = \frac{d\vec{p}}{dt}$$

Question 16

A beanbag bear and a rubber ball, each of mass $$m$$, are dropped from the same height with the same speed $$V$$ and hit the floor. The bear comes to rest, while the ball bounces upward with speed $$V. $$What is the change in momentum for the ball?

Accepted Answer

$$2mV ($$upward)

Question 17

Which of the following best describes the effect of internal forces on the total momentum of a system?

Accepted Answer

Internal forces cannot change the total momentum of a system.

Question 18

Two football players, one running north and the other running east, collide and stick together. How do you determine the direction of their combined motion after the collision?

Accepted Answer

By adding their momentum vectors using vector addition.

Question 19

Which of the following is a correct statement about collisions?

Accepted Answer

Momentum is always conserved in a collision, but kinetic energy may not be.

Chapter 8: Linear Momentum and Collisions – Study Notes

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