Practice Gravity in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The universal attractive force between any two objects with mass, decreasing with the square of distance.

Everything pulls on everything else—but only huge things (like Earth) pull noticeably.

Showing a random 20 of 50 problems.

Example 1

medium
A rock dropped from rest falls for 4 s4\text{ s} (g=10g=10). Find the distance fallen.

Example 2

hard
An object falls from rest and reaches the ground at 30 m/s30 \text{ m/s}. From what height was it dropped? Use g=9.8 m/s2g = 9.8 \text{ m/s}^2, no air resistance.

Example 3

hard
If a planet's radius shrinks to half its current value but its mass stays the same, what happens to surface gg?

Example 4

medium
A rock is dropped from rest and falls for 5 s5 \text{ s}. How far does it fall? Use g=9.8 m/s2g = 9.8 \text{ m/s}^2, no air resistance.

Example 5

medium
An object weighs 80 N80\text{ N} on Earth. At an altitude where gg is one-quarter as strong, find its weight.

Example 6

medium
If Earth's mass were doubled but its radius stayed the same, what would gg become?

Example 7

easy
An object weighs 200 N200 \text{ N} on Earth. What is its mass? Use g=9.8 m/s2g = 9.8 \text{ m/s}^2.

Example 8

challenge
On a planet, a 2 kg2\text{ kg} ball dropped from rest falls 20 m20\text{ m} in 2 s2\text{ s}. Find that planet's gg.

Example 9

hard
The Moon orbits Earth at r=3.84×108 mr = 3.84 \times 10^8 \text{ m} with mass 7.35×1022 kg7.35 \times 10^{22} \text{ kg}. Find the gravitational force between Earth (M=5.97×1024 kgM = 5.97 \times 10^{24} \text{ kg}) and the Moon. Use G=6.674×10−11 N m2/kg2G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2.

Example 10

medium
Is gravitational force a push or a pull?

Example 11

medium
If the distance between two masses triples, by what factor does the gravitational force change?

Example 12

challenge
At what distance from Earth's center is the gravitational force on a 1 kg1 \text{ kg} mass equal to 1 N1 \text{ N}? Use G=6.674×10−11 N m2/kg2G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2 and Earth's mass M=5.97×1024 kgM = 5.97 \times 10^{24} \text{ kg}.

Example 13

easy
Is gravity a contact force or a non-contact (field) force?

Example 14

medium
Find the gravitational force between a 10 kg10\text{ kg} and a 20 kg20\text{ kg} mass 2 m2\text{ m} apart (G=6.67×10−11G=6.67\times 10^{-11}).

Example 15

hard
How high above Earth's surface does gg drop to 9.0 m/s29.0 \text{ m/s}^2? Take RE=6.37×106 mR_E = 6.37 \times 10^6 \text{ m} and surface g=9.8 m/s2g = 9.8 \text{ m/s}^2.

Example 16

easy
Find the weight of a 10 kg10 \text{ kg} object near Earth's surface. Use g=9.8 m/s2g = 9.8 \text{ m/s}^2.

Example 17

medium
Two identical 80 kg80 \text{ kg} people stand 0.5 m0.5 \text{ m} apart. Find the gravitational attraction. Use G=6.674×10−11 N m2/kg2G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2.

Example 18

medium
Two objects of mass 1 kg1 \text{ kg} and 2 kg2 \text{ kg} are dropped from the same height (no air resistance). Which hits the ground first?

Example 19

medium
Two 50 kg50\text{ kg} masses are 5 m5\text{ m} apart (G=6.67×10−11G=6.67\times 10^{-11}). Find the gravitational force between them.

Example 20

hard
Two stars of mass 2×1030 kg2 \times 10^{30} \text{ kg} each are 1×1011 m1 \times 10^{11} \text{ m} apart. Find the gravitational force between them. Use G=6.674×10−11 N m2/kg2G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2.
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