Calculating Mass

Solving for Force

​Force= Mass x Gravity

A 75 kg ball is dropped from the roof of the school. How much force is acting on the ball?
Force= ?

Mass= 75 kg
Gravity= 9.8m/s/s Force= 75kg x 9.8m/s/s = 735N

Solving for Mass

​Mass= Force/Gravity

A bowling ball fell from a bridge with 490N of force. What is the mass of the bowling ball?
Force= 490N

Mass=?
Gravity= 9.8m/s/s Mass= 490N / 9.8m/s/s = 50kg

Solving for Weight

​Weight= Mass x gravity

What is the weight of an object (on earth) that has a mass of 64kg?

Mass= 64kg

Gravity= 9.8m/s/s

Weight=?

Weight= 64kg x 9.8m/s/s = 627N

Notice

Notice how the formula for solving for Force and solving for weight is the same. But also, notice how if an astronaut goes to the moon, his mass remains the same but his weight decreases. This is because he got further away from earth, the acceleration of gravity decreases.

Multiple Choice

What is the force on a 1kg ball that is falling freely due to the pull of gravity? (9.8m/s/s)

• 34N

• 9.8N

• 12N

• 9.8kg

Multiple Choice

What is the mass of a person who weighs 500N

• 500kg

• 50,000kg

• 51kg

• 1kg

Multiple Choice

What is the weight of an object (on earth) that has a mass of 45kg?

• 441N

• 435N

• 4.6N

• 4.5N

Multiple Choice

What is the weight of an object (on the moon) that has a mass of 151kg?

Gravity on the moon= 1.62 m/s/s

• 91N

• 93.2N

• 200N

• 244.6N

How Much do you Weigh?

​1 kilogram = 2.2 pounds

To find your mass in kg, take your weight in pounds and divide by 2.2

Example: My mass is 200 pounds, so I would divide 200/2.2 = 90.9kg

My mass on the moon (Grav= 1.6) would still be 90.9kg but my weight would be 145.4N

Multiple Choice

What is the force on a 321kg machine that is free falling on earth? (9.8m/s/s)

• 3,145.8N

• 3,140N

• 8,541.3N

• 321N

Page 24 in your Packets

​Complete page 24 in your packet

Make sure adjust your answers based on the gravity of each planet.