Q: A 2 kg ball is dropped from rest. How far does it fall in 3 seconds? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

$$d = \frac{1}{2}gt^2$ = \frac{1}{2} \times 9.8 \times 3^2$ = 44.1\ \mathrm{m}$$

Q: A 10 kg object weighs 98 N on Earth. What would its weight be on a planet where $$g = 3.7\ \mathrm{m/s^2$} ($$like Mars)?

$$W = mg = 10 \times 3.7 = 37\ \mathrm{N}$$

Q: If two equal forces of 10 N act at an angle of 60° to each other, what is the magnitude of the resultant force?

$$F_{\mathrm{res}} = \sqrt{10^2$ + 10^2$ + 2 \times 10 \times 10 \times \cos 60^\circ} = \sqrt{100 + 100 + 100} = \sqrt{300} \approx 17.3\ \mathrm{N}$$

Question 1

Which of the following statements best describes why a scientific hypothesis must be falsifiable?

Accepted Answer

Because it must be possible to prove the hypothesis is incorrect through experiment or observation.

Question 2

A car travels around a circular track at a constant speed of 20 m/s. Which statement is correct about the car's acceleration?

Accepted Answer

The car is accelerating because its velocity is changing direction.

Question 3

A 5 kg object is acted on by a net force of 15 N. What is its acceleration?

Accepted Answer

$$a = \frac{F}{m} = \frac{15}{5} = 3\ \mathrm{m/s^2$}$$

Question 4

Which of the following quantities is a scalar?

Accepted Answer

Mass

Question 5

A box is pushed across a floor at constant velocity. If the applied force is 40 N, what is the friction force?

Accepted Answer

40 N, opposite to the direction of motion

Question 6

A 2 kg ball is dropped from rest. How far does it fall in 3 seconds? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$d = \frac{1}{2}gt^2$ = \frac{1}{2} 	imes 9.8 	imes 3^2$ = 44.1\ \mathrm{m}$$

Question 7

Which of the following best explains why the normal force does no work on an object sliding across a horizontal surface?

Accepted Answer

Because the normal force acts perpendicular to the direction of motion

Question 8

A 10 kg object weighs 98 N on Earth. What would its weight be on a planet where $$g = 3.7\ \mathrm{m/s^2$} ($$like Mars)?

Accepted Answer

$$W = mg = 10 	imes 3.7 = 37\ \mathrm{N}$$

Question 9

Which of the following is an example of energy conversion due to friction?

Accepted Answer

A car's brakes heating up as it slows down

Question 10

If two equal forces of 10 N act at an angle of 60° to each other, what is the magnitude of the resultant force?

Accepted Answer

$$F_{\mathrm{res}} = \sqrt{10^2$ + 10^2$ + 2 	imes 10 	imes 10 	imes \cos 60^\circ} = \sqrt{100 + 100 + 100} = \sqrt{300} \approx 17.3\ \mathrm{N}$$

Question 11

A spring stretches 0.2 m when a force of 4 N is applied. What is the spring constant $$k$$?

Accepted Answer

$$k = \frac{F}{x} = \frac{4}{0.2} = 20\ \mathrm{N/m}$$

Question 12

Which of the following energy sources does NOT ultimately originate from solar energy?

Accepted Answer

Geothermal energy

Question 13

A 1 kg ball is thrown straight up with an initial velocity of 20 m/s. What is its kinetic energy at launch?

Accepted Answer

$$KE = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 1 	imes 20^2$ = 200\ \mathrm{J}$$

Question 14

Which of the following best describes how Neptune was discovered?

Accepted Answer

By observing disturbances in the orbit of Uranus

Question 15

A 50 kg astronaut weighs 490 N on Earth. What is her mass on the Moon, where $$g = 1.6\ \mathrm{m/s^2$}$$?

Accepted Answer

50 kg

Question 16

Which formula correctly gives the gravitational force between two masses $$M$$ and $$m$$ separated by distance $$r$$?

Accepted Answer

$$F = \frac{GMm}{r^2$}$$

Question 17

A 2 kg object moves with a constant velocity of 5 m/s. What is the net force acting on it?

Accepted Answer

0 N

Question 18

A 3 kg object is accelerated from rest to 6 m/s in 2 seconds. What is the average net force applied?

Accepted Answer

$$a = \frac{\Delta v}{\Delta t} = \frac{6}{2} = 3\ \mathrm{m/s^2$}$$, $$F = ma = 3 	imes 3 = 9\ \mathrm{N}$$

Question 19

Which of the following statements is true about mass and weight?

Accepted Answer

Mass remains constant, but weight changes with gravity.

Question 20

A 4 kg object is lifted 5 meters vertically. How much work is done against gravity? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$W = Fd = mgd = 4 	imes 9.8 	imes 5 = 196\ \mathrm{J}$$

PHY101 Exam-1 Study Guide: Foundations of Mechanics and Gravity

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