# Three classical mechanics problems

(See attached file for full problem description)

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1. A rock is thrown straight up from the earth's surface. Which one of the following statements concerning the net force acting on the rock at the top of its path is true?

A It is equal to the weight of the rock.

B It is instantaneously equal to zero newtons.

C Its direction changes from up to down.

D It is greater than the weight of the rock.

E It is less than the weight of the rock, but greater than zero newtons.

2. Two point masses m and M are separated by a distance d. If the distance between the masses is increased to 3d, how does the gravitational force between them change?

A The force will be one-third as great.

B The force will be one-ninth as great.

C The force will be three times as great.

D The force will be nine times as great.

E It is impossible to determine without knowing the numerical values of m, M, and d.

3. Which one of the following statements concerning the two "gravitational constants" G, the universal gravitational constant, and g the magnitude of the acceleration due to gravity is true?

A The values of g and G do not depend on location.

B The values of g and G depend on location.

C The value of G is the same everywhere in the universe, but the value of g is not.

D The value of g is the same everywhere in the universe, but the value of G is not.

E The values of g and G are equal on the surface of any planet, but in general, vary with location in the universe.

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(See attached file for full problem description)

#### Solution Summary

Three problems. One is about a rock being thrown straight up. The other two are about the forces of gravity and gravitational constants between two masses.