# Circular motion problem

1. Nov 15, 2008

### phys1618

1. The problem statement, all variables and given/known data

If John was stationary in space at eh same distance fromo the sun as the earth is, a.how much force would teh sun be exeerting on John? b.what would be John's acceleration towards the sun? c.what would be the sun's acceleration toward John??

2. Relevant equations
Mass of John= 50kg
Mass of Sun = 2x1030kg
r=1.5x1011m
T=331536000s
Fg=G*Msun Mjohn/r2
a=4pi2r/T2
Fs=force of the sun
Fj=force of john
as=acceleration of sun
aj=acceleration of john

3. The attempt at a solution
a.
Fs=GMsMj/r2
Fs=(6.67X10-11)(2x1030)(50)/(1.5x1011)2
Fs= .2964444444 N

b. aj=4pi2r/T2
aj=4pi2(1.5x1011m)/(31536000s)2
aj= .0059497487m/s2

c. Would I use the same equation as b, with the same T? or is it a different T??

thank you for all helps and comments

2. Nov 16, 2008

### alphysicist

Hi phys1618,

This is right, but there is a more direct method that will also help you in part c. In part a you found the force; what is the relationship between force and acceleration? You should get the same answer.

Then for part c, do the same procedure to find the acceleration for the sun (which will of course be much smaller).

3. Nov 16, 2008

### phys1618

F=ma
yea, it did gave me the same answer as b
so for c. I
Fs=Msun*a of the sun
.2964444444 N=2x10^30kg* a
1.48 x 10^-31 m/s^2=a
right??

thank you for the help!!!

4. Nov 16, 2008