Q: An atomic nucleus at rest decays into an alpha particle and a recoiling nucleus. If the alpha particle's speed is $$2.8 \times 10^5$\ \mathrm{m/s}$$ and the recoiling nucleus has 57 times the mass of the alpha particle, what is the speed of the recoiling nucleus?

$$4.9 \times 10^3$\ \mathrm{m/s}$$

Question 1

The area under the force vs. time curve in the first image represents which physical quantity?

Accepted Answer

The impulse delivered to an object

Question 2

A 0.145-kg baseball is pitched at $$31.0\ \mathrm{m/s}$$ and hit straight back at $$46.0\ \mathrm{m/s}. If $$the contact time is $$5.00 	imes 10$$^{-3}$$\ \mathrm{s}$$, what is the magnitude of the average force exerted by the bat on the ball? (Assume the direction reverses upon impact.)

Accepted Answer

$$2240\ \mathrm{N}$$

Question 3

A small beanbag and a bouncy rubber ball of equal mass are dropped from the same height. Which imparts a greater impulse to the floor?

Accepted Answer

The rubber ball

Question 4

In the rifle recoil example, why does the rifle move backward when the bullet is fired?

Accepted Answer

Because momentum must be conserved, so the rifle recoils with equal and opposite momentum to the bullet

Question 5

A 110-kg tackler moving at $$2.5\ \mathrm{m/s}$$ collides head-on and holds onto an 82-kg halfback moving at $$5.0\ \mathrm{m/s} in $$the opposite direction. What is their mutual speed immediately after the collision?

Accepted Answer

$$1.8\ \mathrm{m/s}$$

Question 6

An atomic nucleus at rest decays into an alpha particle and a recoiling nucleus. If the alpha particle's speed is $$2.8 	imes 10^5$\ \mathrm{m/s}$$ and the recoiling nucleus has 57 times the mass of the alpha particle, what is the speed of the recoiling nucleus?

Accepted Answer

$$4.9 	imes 10^3$\ \mathrm{m/s}$$

Question 7

In a perfectly inelastic collision, two identical boxes stick together after colliding. If one box slides at $$10\ \mathrm{m/s}$$ and the other is at rest, what is their final velocity?

Accepted Answer

$$5\ \mathrm{m/s}$$

Question 8

On a frictionless surface, a sliding box collides and sticks to a second identical box at rest. What is the final kinetic energy of the system in terms of the initial kinetic energy?

Accepted Answer

$$KE_f = KE_i / 2$$

Question 9

Where is the center of mass of a baseball bat located?

Accepted Answer

Closer to the thin end (near handle)

Question 10

A rocket at rest in space fires its engines and expels gas at high speed. According to the conservation of momentum, what happens to the rocket?

Accepted Answer

It moves in the opposite direction to the expelled gas

Question 11

In an elastic collision between two objects of equal mass in one dimension, what happens to their velocities?

Accepted Answer

They exchange velocities

Question 12

A box slides with initial velocity $$v_i on a $$frictionless surface and collides inelastically with an identical box at rest. What is the final velocity $$v_f of $$the combined boxes?

Accepted Answer

$$v_f = v_i/2$$

Question 13

In the context of impulse, which of the following statements is correct?

Accepted Answer

Impulse is the area under the force vs. time curve

Question 14

In a collision, the total momentum of a system is conserved if:

Accepted Answer

There are no external forces acting on the system

Question 15

A golf ball with speed $$v$$ hits a stationary bowling ball head-on (situation 1). A bowling ball with speed $$v$$ hits a stationary golf ball head-on (situation 2). In which case does the golf ball have the greater speed after the collision?

Accepted Answer

Situation 2

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