Gravitation
You can use the interactive calculator on page 216 of your e-Book to check your work.
1. Determine the force of gravity between two 3.0 kg masses held 1.0 m apart.
2. Determine the force of gravity between the Earth (5.98 × 1024 kg) and a 70 kg person standing on
Earth’s surface. The radius of Earth is 6.38 × 106 m. Compare this value to the person’s weight.
3. The mass of the Moon is 7.34 × 1022 kg and its radius is 1.74 × 106 m. If a 30 kg dog stands on the
surface of the Moon, how much does he weigh? (What is the force of gravity on him?)
4. Calculate the force of attraction between the Earth and an alien space ship orbiting at a radius of
20,000 km. Earth has a mass of 5.98 × 1024 kg, and the spaceship has a mass of mship= 500,000 kg.
(Hint: be careful with units!)
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5. Two identical spheres (of equal mass) a distance of 10 meters apart exert a force of gravity of
0.00050 N on each other. What are their masses?
Conceptual questions
6. Two masses, m1 and m2, are placed a distance d apart.
a. If the masses are both doubled, by what factor does the force of gravity between them change?
A. ¼
B. ½
C. 2
D. 4
b. If the distance between the masses is doubled, by what factor does the force of gravity change?
A. ¼
B. ½
C. 2
D. 4
c. If distance between the masses is reduced to half its value, by what factor does the force of
gravity change?
A. ¼
B. ½
C. 2
D. 4
7. A honeybee is in flight between a flower and its hive. Which of the following statements is true?
A. The bee exerts a force on the Earth equal to the force the Earth exerts on the bee.
B. The Earth exerts a greater force on the bee than the bee exerts on Earth.
C. The bee is in flight, but not in orbit, so there is no force of gravity on it.
D. The bee exerts a greater force on the Earth than the Earth exerts on the bee.
8. Explain, in your own words, how a falling apple led to Newton’s discovery of the law of universal
gravitation.
9. Describe a technology that depends on an understanding of Newton’s universal law of gravitation.
10. Write a multiple-choice equation that requires the reader to understand that the force of gravity
between two objects depends only on the mass of the objects and the distance between them.
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