# Homework Help: Force of gravity problem

1. Mar 23, 2015

### MiniOreo1998

1. The problem statement, all variables and given/known data
A 12 kg meteor experiences an acceleration of 7.2 m/s2, when falling towards the Earth.

A) How high above the Earths’ surface is the meteor?

B) What force will a 30 kg meteor experience at the same altitude?

Starting to get more comfortable with my calculations. If there are any blunders or things I could have done to make my work more clear, any suggestions would be appreciated.

2. Relevant equations
r = √ G m / g

3. The attempt at a solution
A)

r = √ G m / g

r = (6.67 x 10-11) (5.98 x 1024) / 7.2 = 7.4 x 106

7.4 x 106 - 6.38 x 106 = 1060

r = 1060 km

B)

Mass is irrelevant

2. Mar 23, 2015

### Simon Bridge

Well done - I had a slight hesitation there thinking it may be a terminal velocity problem but the distance is too great for that and the context all wrong.

A. finesse the long-answers by writing a sentence stating the result:
"the meteor is 1060km above the Earth's surface".

B. Mass is relevant - the acceleration of gravity does not depend on the mass but the question asks for force.

3. Mar 23, 2015

### haruspex

Right answer, but I would have calculated it using ratio to 9.8m/s2: $(R+x)^2g_{R+x}=R^2g_R$

4. Mar 24, 2015

### MiniOreo1998

Wow, completely misread the question. How embarrassing..

Then F = m a,
F = (30) (7.2)
F = 216 N [toward Earth]