Q: A 50 kg student stands on the surface of the Earth (mass $$5.98 \times 10$$^{24}$$ kg, radius 6.38$$ \times $$10^6 m). $$What is the gravitational force between the student and the Earth? ($$G = 6.67 \times 10$$^{-11}$$ \ \mathrm{N \cdot m^2$ / kg^2$})$$

$$F = 7.7 \times 10^2$ \ \mathrm{N}$$

Question 1

According to Newton's Law of Universal Gravitation, what happens to the gravitational force between two objects if the distance between them is tripled?

Accepted Answer

The force decreases by a factor of 9.

Question 2

Which equation correctly represents Newton's Law of Universal Gravitation?

Accepted Answer

$$F = G \frac{m_1$ m_2$}{r^2$}$$

Question 3

If the mass of one object is doubled and the distance between two objects is halved, by what factor does the gravitational force change?

Accepted Answer

It becomes 8 times greater.

Question 4

A 50 kg student stands on the surface of the Earth (mass $$5.98 	imes 10$$^{24}$$ kg, radius 6.38$$ 	imes $$10^6 m). $$What is the gravitational force between the student and the Earth? ($$G = 6.67 	imes 10$$^{-11}$$ \ \mathrm{N \cdot m^2$ / kg^2$})$$

Accepted Answer

$$F = 7.7 	imes 10^2$ \ \mathrm{N}$$

Question 5

Which of the following best describes the Inverse Square Law as it applies to gravity?

Accepted Answer

The gravitational force is inversely proportional to the square of the distance.

Question 6

A 7 kg rock weighs 11.4 N on the surface of the Moon, which has a radius of $$1.74 	imes 10^6$ m. What is the mass of the Moon? (G = 6.67$$ 	imes $$10^{-11}$$ \ \mathrm{N \cdot $$m^2$$ / $$kg^2$$}$$)

Accepted Answer

$$7.3 	imes 10$$^{22}$$ kg

Question 7

Which of the following statements about gravitational force is correct according to Newton's Third Law?

Accepted Answer

The force you exert on Earth is equal in magnitude and opposite in direction to the force Earth exerts on you.

Question 8

What is the primary reason gravity is only noticeable when at least one of the objects is very massive?

Accepted Answer

The gravitational constant $$G is $$very small.

Question 9

Which of the following best describes a satellite in orbit around the Earth?

Accepted Answer

It is falling toward Earth but has enough tangential velocity to keep missing it.

Question 10

Spring tides occur when:

Accepted Answer

The Sun and Moon are aligned with the Earth.

Question 11

Which of the following is true about neap tides?

Accepted Answer

They occur when the Sun and Moon are perpendicular to each other.

Question 12

What is a singularity in the context of black holes?

Accepted Answer

A point where mass is concentrated with nearly infinite density and almost zero radius.

Question 13

What is the Schwarzschild radius?

Accepted Answer

The radius at which the escape velocity equals the speed of light.

Question 14

Why can't light escape from a black hole?

Accepted Answer

The escape velocity exceeds the speed of light.

Question 15

What is the main cause of ocean tides on Earth?

Accepted Answer

The gravitational pull of the Moon and the Sun.

Question 16

If the core of a star collapses and contains more than about 3 solar masses, what is the likely outcome?

Accepted Answer

A black hole forms.

Question 17

What is perturbation in the context of planetary motion?

Accepted Answer

A change in a planet's orbit due to the gravitational force of another object.

Question 18

Which of the following best explains why the gravitational force between two objects is equal in magnitude but opposite in direction?

Accepted Answer

Newton's Third Law

Question 19

If the distance between two objects is reduced to one-third, what happens to the gravitational force between them?

Accepted Answer

It becomes 9 times greater.

Question 20

Which of the following is NOT a consequence of the Law of Universal Gravitation?

Accepted Answer

Gravity only acts on Earth.

Gravity, Satellites, and Tides: Study Notes for Chapter 9

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