Q: A farmer pulls a sled with a force of 5000 N at an angle of $$36.9^ ext{o}$$ above the horizontal for 20 m. What is the work done by the tractor on the sled?

$$W = 5000 \times \cos 36.9^ ext{o} \times 20$$

Q: If a force is perpendicular to the direction of displacement, what is the work done by the force?

Zero, because $$\cos 90^\text{o} = 0$$

Q: A sled of mass 1500 kg is pulled 20 m with a net work of 10 kJ. If its initial speed is 2.0 m/s, what is its final kinetic energy?

$$K_2$$ = $$K_1 + W$$_{\text{tot}} = 3000 \text{ J} + 10,000 \text{ J} = 13,000 \text{ J}$$

Question 1

An astronaut's weight decreases as they move away from the Earth's surface. Which equation correctly describes the astronaut's weight at a distance $$r$$ from the center of the Earth?

Accepted Answer

$$w = Gm_E m / r^2$

Question 2

A satellite is in a circular orbit around the Earth. Which force provides the centripetal acceleration required to keep the satellite in orbit?

Accepted Answer

The Earth's gravitational force

Question 3

A farmer pulls a sled with a force of 5000 N at an angle of $$36.9^	ext{o}$$ above the horizontal for 20 m. What is the work done by the tractor on the sled?

Accepted Answer

$$W = 5000 	imes \cos 36.9^	ext{o} 	imes 20$$

Question 4

Which of the following statements about kinetic energy is correct?

Accepted Answer

Kinetic energy depends on the mass and the square of the speed of the object.

Question 5

A weightlifter holds a barbell stationary above their head. What is the work done by the weightlifter on the barbell?

Accepted Answer

Zero, because the displacement is zero.

Question 6

A package of mass $$m$$ slides down a frictionless ramp of height $$h$$ inclined at angle $$\beta. $$What is the total work done by all forces on the package?

Accepted Answer

$$W = mgh$$

Question 7

Which equation represents the work-energy theorem?

Accepted Answer

$$W_{	ext{tot}} = K_2$ - K_1$

Question 8

A spring is compressed by 0.01 m under a force of 600 N. What is the force constant $$k of $$the spring?

Accepted Answer

$$k = 600 / 0.01$$

Question 9

Which of the following best describes the conservation of mechanical energy for a system under only gravitational forces?

Accepted Answer

The sum of kinetic and potential energy remains constant.

Question 10

A projectile is launched from point A toward B with increasing initial speed. Which trajectory will result in the projectile entering a stable orbit around the Earth?

Accepted Answer

The trajectory where the projectile's speed matches the orbital speed for its altitude.

Question 11

What is the work done by a force $$\vec{F}$$ acting at an angle $$\phi to $$the displacement $$\vec{s}$$?

Accepted Answer

$$W = F s \cos \phi$$

Question 12

If a force is perpendicular to the direction of displacement, what is the work done by the force?

Accepted Answer

Zero, because $$\cos 90^	ext{o} = 0$$

Question 13

A sled of mass 1500 kg is pulled 20 m with a net work of 10 kJ. If its initial speed is 2.0 m/s, what is its final kinetic energy?

Accepted Answer

$$K_2$$ = $$K_1 + W$$_{	ext{tot}} = 3000 	ext{ J} + 10,000 	ext{ J} = 13,000 	ext{ J}$$

Question 14

Which of the following is true about the work done by friction when a sled is pulled along level ground?

Accepted Answer

The work is negative because friction opposes the motion.

Question 15

A weightlifter lowers a barbell to the floor. What type of work do the weightlifter's hands do on the barbell?

Accepted Answer

Negative work, because the force is opposite to the displacement.

Question 16

Which equation represents the kinetic energy of a particle?

Accepted Answer

$$K = \frac{1}{2} m v^2$

Question 17

A spring follows Hooke's law. What is the work done by stretching a spring from $$x = 0 to$$ $$x$$?

Accepted Answer

$$W = \frac{1}{2} k x^2$

Question 18

Which of the following best describes the energy transformation when a basketball falls from a height?

Accepted Answer

Gravitational potential energy is converted to kinetic energy.

Question 19

Which statement about black holes is correct?

Accepted Answer

If all the mass of a body lies inside the Schwarzschild radius, no light can escape from it.

Circular Motion, Gravitation, Work, and Energy – Study Notes for College Physics

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