Q: A 90 lb gymnast stands on a scale on Earth. What is her mass in kilograms? (Use $$1 \ \mathrm{lb} = 0.454 \ \mathrm{kg})$$

$$90 \times 0.454 = 40.86 \ \mathrm{kg}$$

Q: If a 70 kg person is standing in an elevator accelerating upward at $$2.0 \ \mathrm{m/s^2$}$$, what is their apparent weight?

$$W_{\mathrm{app}} = mg + ma = 70 \times 9.8 + 70 \times 2.0 = 826 \ \mathrm{N}$$

Q: A 240 lb football player is standing on a scale in an elevator that is accelerating downward at $$1.5 \ \mathrm{m/s^2$}. $$What is his apparent weight in newtons? (Use $$1 \ \mathrm{lb} = 4.45 \ \mathrm{N}$$, $$g = 9.8 \ \mathrm{m/s^2$})$$

$$W_{\mathrm{app}} = 240 \times 4.45 \times \left(1 - \frac{1.5}{9.8}\right) = 1070 \times 0.847 = 907 \ \mathrm{N}$$

Question 1

Which of the following statements correctly distinguishes between mass and weight?

Accepted Answer

Mass is an intrinsic property of matter, while weight is the gravitational force acting on that mass.

Question 2

A 90 lb gymnast stands on a scale on Earth. What is her mass in kilograms? (Use $$1 \ \mathrm{lb} = 0.454 \ \mathrm{kg})$$

Accepted Answer

$$90 	imes 0.454 = 40.86 \ \mathrm{kg}$$

Question 3

If a 70 kg person is standing in an elevator accelerating upward at $$2.0 \ \mathrm{m/s^2$}$$, what is their apparent weight?

Accepted Answer

$$W_{\mathrm{app}} = mg + ma = 70 	imes 9.8 + 70 	imes 2.0 = 826 \ \mathrm{N}$$

Question 4

A 1000 kg elevator is at rest. As it starts moving, a passenger measures an apparent weight of 600 N for the first 3 seconds. What is the acceleration of the elevator during this time? (Assume $$g = 9.8 \ \mathrm{m/s^2$}$$ and the passenger's mass is 60 kg.)

Accepted Answer

$$a = \frac{W_{\mathrm{app}} - mg}{m} = \frac{600 - 588}{60} = 0.2 \ \mathrm{m/s^2$}$$

Question 5

Which of the following best describes the concept of 'apparent weight'?

Accepted Answer

It is the normal force exerted by a supporting surface, which can differ from the actual weight if the object is accelerating.

Question 6

A 240 lb football player is standing on a scale in an elevator that is accelerating downward at $$1.5 \ \mathrm{m/s^2$}. $$What is his apparent weight in newtons? (Use $$1 \ \mathrm{lb} = 4.45 \ \mathrm{N}$$, $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$W_{\mathrm{app}} = 240 	imes 4.45 	imes \left(1 - \frac{1.5}{9.8}ight) = 1070 	imes 0.847 = 907 \ \mathrm{N}$$

Question 7

Which of the following scenarios would result in a person experiencing 'weightlessness'?

Accepted Answer

Floating inside the International Space Station in orbit around Earth.

Question 8

A 70 kg astronaut is in free fall inside a spacecraft orbiting Earth. What is her apparent weight?

Accepted Answer

$$W_{\mathrm{app}} = 0 \ \mathrm{N}$$

Question 9

If a person feels heavier than normal while standing in an elevator, which of the following must be true?

Accepted Answer

The elevator is accelerating upward.

Question 10

A 150 lb professor stands on a scale in an elevator. The scale reads 670 N. What is the acceleration of the elevator? (Use $$1 \ \mathrm{lb} = 4.45 \ \mathrm{N}$$, $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$a = \frac{n - mg}{m} = \frac{670 - 667.5}{68.1} = 0.04 \ \mathrm{m/s^2$}$$ upward

Question 11

Which of the following best explains why astronauts in the International Space Station appear weightless?

Accepted Answer

They are in free fall, so their apparent weight is zero.

Question 12

A 70 kg person is standing in an elevator that is slowing down as it moves downward. The scale reads 750 N. What is the acceleration of the elevator?

Accepted Answer

$$a = \frac{W_{\mathrm{app}} - mg}{m} = \frac{750 - 686}{70} = 0.91 \ \mathrm{m/s^2$}$$ upward

Question 13

If the acceleration due to gravity on Jupiter is $$24.8 \ \mathrm{m/s^2$}$$, what would be the weight of a 60 kg object on Jupiter?

Accepted Answer

$$W = 60 	imes 24.8 = 1488 \ \mathrm{N}$$

Question 14

A 50 kg person is in an elevator in free fall. What does the scale read?

Accepted Answer

0 N

Question 15

Which of the following is a correct unit conversion for force?

Accepted Answer

$$1 \ \mathrm{N} = 0.225 \ \mathrm{lb}$$

Question 16

A 100 kg astronaut weighs 980 N on Earth. What would be his mass and weight on the Moon, where $$g_{\mathrm{moon}} = 1.6 \ \mathrm{m/s^2$}$$?

Accepted Answer

Mass: 100 kg, Weight: $$100 	imes 1.6 = 160 \ \mathrm{N}$$

Question 17

A 60 kg person stands on a scale in an elevator that is moving upward at constant velocity. What does the scale read?

Accepted Answer

$$W_{\mathrm{app}} = 60 	imes 9.8 = 588 \ \mathrm{N}$$

Question 18

If a 70 kg person is in an elevator accelerating downward at $$3.0 \ \mathrm{m/s^2$}$$, what is their apparent weight?

Accepted Answer

$$W_{\mathrm{app}} = mg - ma = 70 	imes (9.8 - 3.0) = 70 	imes 6.8 = 476 \ \mathrm{N}$$

Question 19

Which of the following is true about mass and weight on different planets?

Accepted Answer

Mass stays the same, but weight changes depending on the gravitational acceleration.

Mass and Weight: Concepts, Calculations, and Applications

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