Q: A box is pulled 10 meters across a floor by a force of 20 N at an angle of $$60^\circ$$ above the horizontal. How much work is done by the force?

$$W = 20\ \mathrm{N} \times 10\ \mathrm{m} \times \cos 60^\circ = 100\ \mathrm{J}$$

Q: A spring with a spring constant $$k = 200\ \mathrm{N/m} is $$compressed by $$0.1\ \mathrm{m}. $$What is the elastic potential energy stored in the spring?

$$U_s = 0.5 \times 200 \times (0.1)^2$ = 1\ \mathrm{J}$$

Q: A 0.5 kg ball is dropped from a height of 10 m. What is its speed just before hitting the ground? (Ignore air resistance, $$g = 9.8\ \mathrm{m/s^2$})$$

$$v = \sqrt{2gh} = \sqrt{2 \times 9.8 \times 10} = 14\ \mathrm{m/s}$$

Question 1

Which of the following best describes the Law of Conservation of Energy for an isolated system?

Accepted Answer

The total energy of the system remains constant, but energy can be transformed between different forms within the system.

Question 2

A 5 kg object is lifted vertically by 3 meters. What is the change in its gravitational potential energy? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta U_g = 147\ \mathrm{J}$$

Question 3

Which of the following forces does NO work on an object?

Accepted Answer

A force that acts perpendicular to the displacement.

Question 4

A box is pulled 10 meters across a floor by a force of 20 N at an angle of $$60^\circ$$ above the horizontal. How much work is done by the force?

Accepted Answer

$$W = 20\ \mathrm{N} 	imes 10\ \mathrm{m} 	imes \cos 60^\circ = 100\ \mathrm{J}$$

Question 5

Which of the following is an example of energy transformation within a system?

Accepted Answer

A moving car's kinetic energy is converted to thermal energy by friction in the brakes.

Question 6

A spring with a spring constant $$k = 200\ \mathrm{N/m} is $$compressed by $$0.1\ \mathrm{m}. $$What is the elastic potential energy stored in the spring?

Accepted Answer

$$U_s = 0.5 	imes 200 	imes (0.1)^2$ = 1\ \mathrm{J}$$

Question 7

A 2 kg cart and a 4 kg cart are both pushed with the same force for the same distance, starting from rest. After the force is removed, which cart has more kinetic energy?

Accepted Answer

Both have the same kinetic energy

Question 8

A force of 15 N acts on an object at an angle of $$90^\circ to $$its displacement. What is the work done by the force?

Accepted Answer

$$W = 0$$

Question 9

Which of the following statements about work and energy is correct?

Accepted Answer

Both work and energy are scalar quantities.

Question 10

A hiker climbs a mountain along two different paths to the same height. Which statement is true about the change in gravitational potential energy?

Accepted Answer

The change in gravitational potential energy depends only on the change in height.

Question 11

A 0.5 kg ball is dropped from a height of 10 m. What is its speed just before hitting the ground? (Ignore air resistance, $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$v = \sqrt{2gh} = \sqrt{2 	imes 9.8 	imes 10} = 14\ \mathrm{m/s}$$

Question 12

Which of the following is NOT a form of energy discussed in the basic energy model?

Accepted Answer

Magnetic energy

Question 13

A force of 50 N is applied to push a box 5 m across a rough floor. If the friction force is 20 N, what is the net work done on the box?

Accepted Answer

$$W_{net} = (50 - 20) 	imes 5 = 150\ \mathrm{J}$$

Question 14

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

Accepted Answer

The net work done on an object is equal to the change in its kinetic energy.

Question 15

A match is struck and ignites. Which energy transformation is primarily taking place?

Accepted Answer

Chemical energy to thermal energy

Question 16

A slingshot is pulled back, stretching the elastic band. What type of energy is primarily stored in the band?

Accepted Answer

Elastic (spring) potential energy

Question 17

A force acts opposite to the direction of an object's displacement. What is the sign of the work done by the force?

Accepted Answer

Negative

Question 18

Which of the following scenarios results in an increase in the system's thermal energy?

Accepted Answer

A block slides across a rough surface and comes to rest.

Question 19

A wind turbine blade rotates with angular velocity $$\omega. If $$the moment of inertia is $$I$$, what is the rotational kinetic energy?

Accepted Answer

$$K_{rot} = \frac{1}{2} I \$$omega^2$$

Chapter 10: Energy and Work – Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드