Instructor’s Copy
Worksheet: Weight = mass X gravity
Weight is a measure of the gravitational force between the object and the Earth. The acceleration of
gravity on Earth is 9.8 m/sec2. Weight is measured in units of Newtons. If one object has more mass
than another then it weighs ( more / less ) than the other object.
As an astronaut goes to the moon, his mass remains the same but his weight decreases. This is
because as he got further away from the Earth, the acceleration of gravity decreases.
Part 1: Weight Problems – acceleration and gravity are the same thing so F=ma is the same as
F=mg.
1. Force (F) = ?
Mass (m) = 75 kg
Gravity (g) = 9.8 m/s/s
2. Force (F) = 490N
Mass (m) = ?
Gravity (g) = 9.8 m/s/s
Formula: F = mg
Formula: m = F/g
Substitution: F = (75 kg)(9.8 m/s2)
Substitution: m = 490 N/9.8 m/s2
Answer: 735 N
Answer: 50 kg
3. What is the force on a 1 kg ball that is falling freely due to the pull of gravity?
Force (F) = ?
Formula: F = mg
Mass (m) = 1 kg
Substitution: F = (1 kg)(9.8 m/s2)
Gravity (g) = 9.8 m/s2 (assumed on Earth)
Answer: 9.8 N
4. What is the mass of a person who weighs 500 N?
Force (F) = 500 N
Formula: m = F/g
Mass (m) = ?
Substitution: m = 500 N/9.8 m/s2
Gravity (g) = 9.8 m/s2
Answer: 51 kg
5. What is the weight of an object (on earth) that has a mass of 45 kg?
Force (F) = ?
Formula: F = mg
Mass (m) = 45 kg
Substitution: F = (45 kg)(9.8 m/s2)
Gravity (g) = 9.8 m/s2
Answer: 441 N
6. The value of gravitational pull on the moon is 1.6 m/s/s. What is the weight of a 75 kg
astronaut on the moon?
Force (F) = ?
Formula: F = mg
Mass (m) = 75 kg
Substitution: F = (75 kg)(1.6 m/s2)
Gravity (g) = 1.6 m/s2
Answer: 120 N
7. A space ship has a mass of 9000 kg. The space ship is launched from Earth and lands on a
distant planet where it has a weight of 390000 N. What is the acceleration of gravity on this
planet?
Force (F) = 390000 N
Formula: g = F/m
Mass (m) = 9000 kg
Substitution: g = 390000 N/9000 kg
Gravity (g) = ?
Answer: 43.3 m/s2
8. Big Bertha tips the scales at 950 Newtons. What is her mass?
Force (F) = 950 N
Formula: m = F/g
Mass (m) = ?
Substitution: m = 950 N/9.8 m/s2
Gravity (g) = 9.8 m/s2
Answer: 96.9 kg
9. If my mass is 100 kilograms, what is my weight?
Force (F) = ?
Formula: F = mg
Mass (m) = 100 kg
Substitution: F = (100 kg)(9.8 m/s2)
Gravity (g) = 9.8 m/s2
Answer: 980 N
10. The elevator in the new office building warns that it can safely lift 300 kg at one time. If John
(850 N), Betty (530 N), Robert (740 N) and Alice (610 N) all get in the elevator at once, can
the elevator safely carry them up to the third floor? Think! Show all work.
This can be solved 2 different ways.
1. Calculate the weight the elevator can lift using F = mg.
F = (300 kg)(9.8 m/s2) = 2,940 N
Total weight of people = 850 N + 530 N + 740 N + 610 N = 2,730 N so the elevator can
carry all of them at the same time.
2. Calculate the mass the elevator can lift using m = F/g.
M = 2,730 N (total weight of the people)/9.8 m/s2 = 278.6 kg so the elevator can carry all
of them at the same time.