8. Centripetal Forces & Gravitation

Newton's Law of Gravity

8. Centripetal Forces & Gravitation

# Newton's Law of Gravity - Video Tutorials & Practice Problems

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concept

## Universal Law of Gravitation

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2

Problem

Problem Two spheres are separated by 10m. If the lighter 40kg sphere feels a gravitational force of 1.6 × 10^{-9} N, what is the mass of the heavier sphere?

A

6 kg

B

9.6 kg

C

60 kg

D

10 kg

3

example

## Where is Net Force on middle object zero?

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4

Problem

ProblemTwo spheres of mass 300 kg and 500 kg are placed in a line 20 cm apart. If another sphere of mass 200 kg is placed between them, 8 cm from the 300 kg sphere, what is the net gravitational force on the 200 kg sphere?

A

-7.32×10

^{-4}N (toward 300kg sphere)B

-1.62×10

^{-4}N (toward 300kg sphere)C

7.32×10

^{-4}N (toward 500kg sphere)D

1.62×10

^{-4}N (toward 500kg sphere)5

concept

## Center of Mass Distance

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6

example

## Find force between spheres with radii

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7

Problem

ProblemA 2,000-kg spacecraft is blasting away from the surface of an unknown planet the same size as the Earth. At 1500km above the surface, an instrument onboard reads the gravitational force to be 18000 N. What is the planet's mass?

A

8.36×10

^{24}kgB

2.89×10

^{12}kgC

1.67×10

^{28}kgD

5.78×10

^{15}kg## Do you want more practice?

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PRACTICE PROBLEMS AND ACTIVITIES (11)

- What is the ratio of the sun's gravitational force on you to the earth's gravitational force on you?
- The point masses m and 2m lie along the x-axis, with m at the origin and 2m at x = L. A third point mass M is ...
- Find the magnitude and direction of the net gravitational force on mass A due to masses B and C in Fig. E13.6....
- Two uniform spheres, each with mass M and radius R, touch each other. What is the magnitude of their gravitati...
- A typical adult human has a mass of about 70 kg. (a) What force does a full moon exert on such a human when it...
- Two spherical objects have a combined mass of 150 kg. The gravitational attraction between them is 8.00 x 10⁻⁶...
- What is the force of attraction between a 50 kg woman and a 70 kg man sitting 1.0 m apart?
- Two 65 kg astronauts leave earth in a spacecraft, sitting 1.0 m apart. How far are they from the center of the...
- The International Space Station orbits 300 km above the surface of the earth. What is the gravitational force ...
- Two uniform spheres, each of mass 0.260 kg, are fixed at points A and B (Fig. E13.5). Find the magnitude and d...
- What is the net gravitational force on the 20.0 kg mass in FIGURE P13.36? Give your answer using unit vectors.