Everything Science Grade 11

12.4 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

Since it doesn’t matterwhat mois, this tells us that theacceleration on a body(due to the Earth’s
gravity) does not depend on the mass of the body. Thus all objects experience the same gravitational
acceleration. The force on different bodies will be different but the acceleration will be the same.Due
to the fact that this acceleration caused by gravity is the same on allobjects we label it differently,
instead of using a we use g which we call the gravitational acceleration.

Comparative Problems ESBFE

Comparative problems involve calculation of something in terms of something else that we know. For
example, if you weigh 490 N on Earth and the gravitational accelerationon Venus is 0,903 that of the
gravitational acceleration on the Earth, then youwould weigh 0,903 x 490 N = 442,5 N on Venus.

Principles for answeringcomparative problems

• Write out equations and calculate all quantitiesfor the given situation


• Write out all relationships between variable from first and second case


• Write out second case


• Substitute all first casevariables into second case


• Write second case in terms of first case

Example 24: Comparative Problem 1

QUESTION

A man has a mass of 70kg. The planet Zirgon isthe same size as the Earth but has twice the

mass of the Earth. What would the man weighon Zirgon, if the gravitational acceleration on

Earth is 9,8 m·s−^2?

SOLUTION

Step 1 : Determine what information has been given

The following has beenprovided:

• the mass of the man, m


• the mass of the planetZirgon (mZ) in terms of the mass ofthe Earth (mE), mZ= 2mE


• the radius of the planet Zirgon (rZ) in terms of the radius of the Earth (rE), rZ= rE

Step 2 : Determine how to approach the problem

We are required to determine the man’s weighton Zirgon (wZ). We can do this

by using:

w = mg = G

m 1 · m 2

r^2

to calculate the weight of the man on Earth andthen use this value to determine

the weight of the man on Zirgon.