Q: A 6.2 kg cannonball is fired straight up at $$44\ \mathrm{m/s}. $$What is its kinetic energy as it leaves the cannon?

$$KE = \frac{1}{2}mv^2$ = \frac{1}{2} \times 6.2 \times 44^2$ = 5998.4\ \mathrm{J}$$

Q: A 16 kg car is moving at $$66\ \mathrm{m/s}. $$What is its momentum?

$$p = mv = 16 \times 66 = 1056\ \mathrm{kg \cdot m/s}$$

Q: On Jupiter's moon Europa, $$g = 2.3\ \mathrm{m/s^2$}. If $$you drop a 6 kg hammer from 40 meters, what is its gravitational potential energy (GPE) before being dropped?

$$GPE = mgh = 6 \times 2.3 \times 40 = 552\ \mathrm{J}$$

Q: A 12 kg car is moving at $$23\ \mathrm{m/s}. If $$the brakes apply a force of $$500\ \mathrm{N} to $$stop the car, what distance will it travel before stopping?

$$d = \frac{mv^2$}{2F} = \frac{12 \times 23^2$}{2 \times 500} = 6.348\ \mathrm{m}$$

Q: A 30,000 kg railroad car is traveling at $$5\ \mathrm{m/s}$$ and collides with a stopped 15,000 kg car. After sticking together, what is their velocity?

$$v = \frac{m_1v_1 + m_2v_2}{m_1$ + m_2$} = \frac{30,000 \times 5}{45,000} = 3.33\ \mathrm{m/s}$$

Question 1

An acorn falls from a tree. As it falls, how do its kinetic energy (KE) and gravitational potential energy (GPE) change?

Accepted Answer

KE increases and GPE decreases.

Question 2

By what factor does the kinetic energy of a car change if its speed is tripled?

Accepted Answer

By a factor of 9

Question 3

A block of mass $$m is $$pulled over a distance $$d by an $$applied force $$F$$ that is parallel to the displacement. What is the work done on the block by the force $$F$$?

Accepted Answer

$$Fd$$

Question 4

A 100 kg diver jumps off a moving boat (500 kg) traveling at 3 m/s. If the diver jumps with a velocity of $$-2 m/s ($$relative to the water), what is the velocity of the boat after the jump? (Assume conservation of momentum.)

Accepted Answer

4 m/s

Question 5

A 350 kg sailboat moves with a momentum of $$16,450\ \mathrm{kg \cdot m/s}. $$What is the velocity of the boat?

Accepted Answer

47 m/s

Question 6

A block of mass $$m is $$moved over a distance $$d by an $$applied force $$F$$ that is perpendicular to the displacement. How much work is done by the force $$F$$?

Accepted Answer

Zero

Question 7

A 4 kg block is attached to a vertical spring with a spring constant $$k = 800\ \mathrm{N/m}. $$The spring stretches $$5\ \mathrm{cm}$$ down. How much elastic potential energy is stored in the system?

Accepted Answer

1.0 J

Question 8

A machine does $$5500\ \mathrm{J} of $$work in $$1$$ minute. What is the power developed by the machine?

Accepted Answer

92 W

Question 9

A 5000 kg sailboat moves with a momentum of $$150,000\ \mathrm{kg \cdot m/s}. $$What is the velocity of the boat?

Accepted Answer

30 m/s

Question 10

A stationary skateboarder I (50 kg) pushes a stationary skateboarder II (75 kg). After the push, skateboarder II moves with a velocity of $$2\ \mathrm{m/s} to $$the left. What is the velocity of skateboarder I?

Accepted Answer

3 m/s to the left

Question 11

A loaded freight car A (36,000 kg) moves at 4 m/s and collides with a stationary car B (10,000 kg). After the collision, the cars stick together. What is their velocity after the collision?

Accepted Answer

3.1 m/s

Question 12

When two objects collide elastically, which of the following is true?

Accepted Answer

Both momentum and kinetic energy are conserved.

Question 13

A 6.2 kg cannonball is fired straight up at $$44\ \mathrm{m/s}. $$What is its kinetic energy as it leaves the cannon?

Accepted Answer

$$KE = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 6.2 	imes 44^2$ = 5998.4\ \mathrm{J}$$

Question 14

A 16 kg car is moving at $$66\ \mathrm{m/s}. $$What is its momentum?

Accepted Answer

$$p = mv = 16 	imes 66 = 1056\ \mathrm{kg \cdot m/s}$$

Question 15

On Jupiter's moon Europa, $$g = 2.3\ \mathrm{m/s^2$}. If $$you drop a 6 kg hammer from 40 meters, what is its gravitational potential energy (GPE) before being dropped?

Accepted Answer

$$GPE = mgh = 6 	imes 2.3 	imes 40 = 552\ \mathrm{J}$$

Question 16

A 12 kg car is moving at $$23\ \mathrm{m/s}. If $$the brakes apply a force of $$500\ \mathrm{N} to $$stop the car, what distance will it travel before stopping?

Accepted Answer

$$d = \frac{mv^2$}{2F} = \frac{12 	imes 23^2$}{2 	imes 500} = 6.348\ \mathrm{m}$$

Question 17

A 30,000 kg railroad car is traveling at $$5\ \mathrm{m/s}$$ and collides with a stopped 15,000 kg car. After sticking together, what is their velocity?

Accepted Answer

$$v = \frac{m_1v_1 + m_2v_2}{m_1$ + m_2$} = \frac{30,000 	imes 5}{45,000} = 3.33\ \mathrm{m/s}$$

Question 18

A block of mass $$m is $$moved over a distance $$d by an $$applied force $$F$$ that is opposite to the displacement. How much work is done by the force $$F$$?

Accepted Answer

$$-Fd$$

Question 19

A big truck collides inelastically with a small car. Which of the following is true about the impulse experienced by each vehicle?

Accepted Answer

They experience the same magnitude of impulse during the collision.

Question 20

A 40 kg skateboarder runs at $$12\ \mathrm{m/s}$$ and jumps off a stationary 8 kg skateboard. What is the velocity of the skateboard after the jump? (Assume conservation of momentum.)

Accepted Answer

10 m/s

Physics Final Exam Review: Energy, Momentum, Work, and Power

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