Conceptual Physics
Mrs. Mills
Ch 12-14 Gravity Practice Problems
Also Ch 9 (circular motion) as well
Fg =
Gm1 m2
2
d
G = 6.67 x 10-11 N m
Mass of Earth = 5.98 x 1024 kg
2
kg
2
Radius of Earth = 6.38 x 106 m
1) Given the mass of two objects and distance between them, you should be able to use the equation
above to find the force of gravity between them. I will NOT help you use your calculator during the
test.
Find the force of gravity between a 45 kg person and the Earth when:
a) the person is standing on the surface of the Earth.
b) the person is 1 Earth radius above the surface of the Earth.
c) The person is at the center of the Earth.
2) If you know the force of gravity acting on an object, you should be able to find the acceleration due to
gravity (F = ma or W=mg). What is the acceleration due to gravity of the person in part a) and b)
above?
3) A gravitational force exists between the Earth and the Sun. Which applies a greater force on the other.
Which will accelerate more?
4) A toy is swung around in a circle at the end of a string. If the string is cut, what path will he follow?
5) The force of gravity acts on all of the apples on a 4 m tall apple tree. Some apples are twice as far
away from the ground as others. These twice as high apples, for the same mass, have
a) 1/4 the weight
b) 1/2 the weight
c) practically the same weight
6) If you stepped in a hole bored completely through the Earth and made no attempt to grab the edges at
either end, what kind of motion would you experience?
7) Explain how your acceleration and velocity change as you go through the hole bored completely
though the Earth.
8) An object has a mass 0.5 kg. It is transported to the surface of Planet Z where the object's weight (Fg)
is measured to be 20 N. The radius of the planet is 4 x 106 m. Determine the acceleration due to
gravity on Planet Z.
9) Using complete sentences, explain why an astronaut on the orbiting space shuttle experiences apparent
weightlessness.
10) If you know the force acting on a object, you should be able to find the acceleration (F = ma)
11) If the moon is constantly being pulled by the Earth, why doesn't it fall into the Earth?
12) Explain how force of gravity between the Earth and Moon is the reason for tides.
13) The Sun's force of gravity on the Earth is about 200 times greater than the Moon's, why is the Moon's
influence on the Earth's tides greater?
14) Who invented gravity?
15) A gravitational force exists between the Earth and the Sun. Which applies a greater force on the other.
Where will acceleration due to gravity be larger?
16) True or False. The force of Earth's gravity on a space shuttle in orbit is zero or nearly zero.
Some Circular Motion Problems
17) Horses that move with the fastest linear speed on a merry-go-round are located where?
18) Centrifugal forces feel real to an observer in a reference frame that is:
a) moving at a constant velocity
b) at rest
c) rotating
19) A new Ferris wheel ride has seats halfway between the axis and the outside rim. Compare the
frequency of the passengers to an ordinary Ferris wheel where the people ride at the outer edge.
20) Can an object accelerate if its velocity is constant? If yes how?
21) Dilbert is driving and Filbert is a passenger. When Dilbert makes a sharp turn to the left, Filbert feels
like he is being pushed to the right. What is the reaction force to this Centrifugal force?
22) A small dog (weight is 50 N) with two broken legs and a strained neck is attached to a 2 meter piece
of string and spun 5 times a second around Elmo's head. What is the dog's linear speed?
23) When you roll a Dixie cup on a table, why does the open end have a greater linear speed?
24) How often does the Earth revolve and around what?
25) Which way does the acceleration of the spinning object point at position B?
26) Which point A or B has a greater frequency?