Q: A couch of mass 20 kg is pushed up a 13 m ramp inclined at $$20^\circ$$ above the horizontal with a force of 50 N applied $$25^\circ$$ below the horizontal. What is the work done by the applied force?

$$W = 50 \times 13 \times \cos(45^\circ)$$

Q: Which of the following best describes the total mechanical energy in a system where only conservative forces act?

$$E = K + U = \text{constant}$$

Q: A force of 10 N is applied at an angle of $$36.9^\circ to $$the direction of displacement, which is 7 m. What is the work done by the force?

$$W = 10 \times 7 \times \cos(36.9^\circ)$$

Question 1

Which of the following correctly expresses the work done by a constant force $$\vec{F}$$ acting over a displacement $$\Delta \vec{r} at an $$angle $$	heta to $$the displacement?

Accepted Answer

$$W = F \Delta r \cos 	heta$$

Question 2

A 2.4 kg box is moved up a ramp inclined at $$30^\circ$$ with a constant frictional force of 14 N over a distance of 3 m. What is the magnitude of the work done by friction?

Accepted Answer

$$42 \ \mathrm{J}$$

Question 3

Which of the following statements about conservative and non-conservative forces is TRUE?

Accepted Answer

Work done by a conservative force is independent of the path taken.

Question 4

A 0.11 kg apple falls from a height of 5.0 m. What is the change in gravitational potential energy as it reaches the ground?

Accepted Answer

$$-5.4 \ \mathrm{J}$$

Question 5

Which of the following is the correct expression for kinetic energy?

Accepted Answer

$$K = \frac{1}{2}mv^2$

Question 6

A couch of mass 20 kg is pushed up a 13 m ramp inclined at $$20^\circ$$ above the horizontal with a force of 50 N applied $$25^\circ$$ below the horizontal. What is the work done by the applied force?

Accepted Answer

$$W = 50 	imes 13 	imes \cos(45^\circ)$$

Question 7

The work-energy theorem states:

Accepted Answer

$$W_{tot} = \Delta K = K_f - K_i$$

Question 8

A box sits at the top of a ramp. It can be moved to the bottom by two different paths: Path 1 (diagonal) and Path 2 (vertical then horizontal). In which case is the work done by gravity greater?

Accepted Answer

The same amount of work is done

Question 9

Which of the following is the correct formula for gravitational potential energy?

Accepted Answer

$$U = mgy$$

Question 10

A 10 kg object is sliding across the floor. If its speed decreases from 8 m/s to 4 m/s due to friction, what is the work done by friction?

Accepted Answer

$$-240 \ \mathrm{J}$$

Question 11

Which of the following best describes the total mechanical energy in a system where only conservative forces act?

Accepted Answer

$$E = K + U = 	ext{constant}$$

Question 12

If the work done by a force is negative, what happens to the kinetic energy of the object?

Accepted Answer

The kinetic energy decreases

Question 13

Which of the following is the correct SI unit for energy?

Accepted Answer

$$\mathrm{kg} \cdot \mathrm{m}^2 / \mathrm{s}^2$$

Question 14

A force is applied perpendicular to the displacement of an object. What is the work done by this force?

Accepted Answer

$$0$$

Question 15

Which of the following is the correct formula for momentum?

Accepted Answer

$$\vec{p} = m \vec{v}$$

Question 16

A 0.11 kg apple falls from rest from a height of 5.0 m. What is its speed just before hitting the ground? (Assume $$g = 9.8 \ \mathrm{m/s}^2)$$

Accepted Answer

$$9.9 \ \mathrm{m/s}$$

Question 17

Which of the following best describes the relationship between work and energy?

Accepted Answer

Work is the process of transferring energy to or from an object by means of a force acting over a distance.

Question 18

If only conservative forces act on a system, which of the following is true?

Accepted Answer

The total mechanical energy remains constant.

Question 19

Which of the following is NOT a requirement for work to be done on an object?

Accepted Answer

The force and displacement must be perpendicular.

Question 20

A force of 10 N is applied at an angle of $$36.9^\circ to $$the direction of displacement, which is 7 m. What is the work done by the force?

Accepted Answer

$$W = 10 	imes 7 	imes \cos(36.9^\circ)$$

Physics Study Guidance: Circular Motion, Projectile Motion, and Work

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