Unit 7 Practice Test

Question 1

For which of the following situations can the equation F = mg not be used to calculate the force due to gravity?

Answer 1

The pull of the Earth’s gravity on the Moon.

Question 2

Two planets exert a gravitational pull on each other. If Planet A has three times more mass than Planet B, what is the pull on Planet B compared to the pull on Planet A ?

Answer 2

The pull on Planet A equals the pull on Planet B.

Question 3

At which of the following distances from the Earth will a spacecraft be beyond the reach of the Earth’s gravitational force?

Answer 3

The spacecraft will never be beyond the reach of the Earth’s gravitational pull.

Question 4

A gravitational force is exerted on a satellite from two different planets as shown in the diagram. Planet A has twice the mass of Planet B, but it is also two times farther from the satellite than Planet B. Which of the following diagrams shows the net force acting on the satellite?

Answer 4

-

Question 5

Consider two balls of masses 100 kg and 200 kg and radii 0.1 m and 0.2 m respectively. Suppose that their centers are separated by 2 m. What is the gravitational force between them?

Answer 5

3.34*10^-7 N

Question 6

Consider two balls of masses 100 kg and 200 kg and radii of 0.1m and 0.2m respectively. The gravitational force between them is 5*10^-7N. What is the shortest distance between the surfaces of the two balls?

Answer 6

1.33 m

Question 7

Consider two asteroids of masses 1.010^15 kg and 3.010^15 kg. Suppose that their centers are separated by 100 km. What is the acceleration of the asteroid with the smaller mass due to the mutual gravitational force?

Answer 7

2.00*10^-5 m/s^2

Question 8

Consider a planet moving around a star in a near-circular orbit. The mass of the star is 6.0*10^35 kg. The period of the planet (the time it takes for the planet to go around the star once) is about 2.5 years. What is the distance between the star and the planet?

Answer 8

1.85*10^13 m

Question 9

In a moving elevator your apparent weight…

Answer 9

increases as the elevator goes up.

Question 10

The average distance between Earth and the Moon is 3.8410^8m. How far from the Earth must a satellite be to have no apparent weight because of the opposing gravitational forces of Earth and the Moon?
^ is 6.6710^-11 Nm^2/kg^2 and the mass of the Earth and Moon are 5.9710^24 kg and 7.2510^22 kg, respectively.

Answer 10

3.46*10^8 m

Question 11

A space shuttle is orbiting the Earth at a distance of 2.00*10^7 m from the Earth’s center. Assuming a circular orbit, find the shuttle’s velocity.

Answer 11

4.46*10^3 m/s

Question 12

a 300 kg meteorite is in circular motion orbiting faraway planet with a speed of 7000 m/s. Its orbit radius is 2.0010^8 m. The planet is composed mostly of an unknown element. The radius of the planet is 110^6 m. Determine the average density of the element in g/cm^3. G is 6.67*10^-11 Nm^2/kg^2

Answer 12

3.51 × 10^4 g / cm^3

Question 13

Consider two balls of masses 100 kg and 200 kg and radii 0.1 m and 0.2 m respectively. Suppose their centers are separated by 2 m. What is the gravitational potential energy of the system?

Answer 13

-6.67*10^-7 J

Question 14

Consider two balls of masses 100 kg and 200 kg and radii 0.1 m and 0.2 m respectively. The gravitational potential energy between them is -5.0*10^-7. What is the shortest distance between the surfaces of the two balls?

Answer 14

2.37 m

Question 15

Consider two balls of the same mass with radii 0.1 m and 0.2 m respectively. The gravitational potential energy between them is -5.0*10^-7. What is the mass of each ball?

Answer 15

1.22*10^2 kg

Question 16

Consider a system consisting of a star and a planet with masses 6.010^36 kg and 9.010^25 kg respectively. They are far away from other stars. Several years ago, the planet was 6.010^15 m away from the star and moving at the speed 4.010^5 m/s (with respect to the star). Now the planet is moving at the speed 5.0*10^5 m/s. How far is it away from the star?

Answer 16

3.58*10^15 m

Question 17

Consider a baseball thrown from the top of a tower on the surface of the Earth. You examine four different launches, each with a larger initial velocity as shown in the illustration. Which of the following concerning the orbital path of the baseball is incorrect?

Answer 17

The first launch results in a parabolic path in which the baseball falls to the surface of the Earth.

Question 18

In order for a satellite in free fall to maintain uniform circular motion, ______________.

Answer 18

there must be a centripetal force

Question 19

You can determine the velocity of a satellite in uniform circular orbit by applying Newton’s second law, Newton’s law of gravity, and the centripetal acceleration due to gravity. Which of the following is not correct?

Answer 19

The satellite’s speed depends on its mass; the larger the mass, the slower the velocity.

Question 20

The moon has a period Tm equal to 28 days and an orbital radius rm equal to 3.8*10^5 km. What is the orbital radius of a satellite that travels around the Earth in 1 day?

Answer 20

4.12 × 10^4 km

Question 21

Planets at a greater distance from the Sun _________________.

Answer 21

have longer periods of revolution

Question 22

Suppose that a new planet is discovered and its period is determined. The new planet’s distance from the Sun could be found using Kepler’s ________________.

Answer 22

third law

Question 23

A satellite of mass m is in circular orbital motion around the Earth, which has mass Me. The distance from the center of the Earth to the satellite is r. Which of the following is the equation for tangential velocity of the satellite?

Answer 23

v = (GMe/r)^1/2

Question 24

The total energy of an orbiting satellite in uniform circular orbit around the Earth ________________.

Answer 24

approaches to zero as r approaches infinity

Question 25

Which of the following best describes the energy of a satellite in uniform circular orbit around the Earth when it moves to a higher orbit?

Answer 25

There is an increase in potential energy and a decrease in kinetic energy