# Gravitational force problem

1. May 23, 2006

### Amith2006

Sir,
Two point masses each equal to 1 kg attract one another with a force of 1 kg.wt. What is the distance between the 2 point masses?
I solved it in the following way:
Here F = 1 kg.wt = 9.8 Newton, m1 = m2 = 1 kg, G = 6.6 x 10^(-11) N.m^2/kg^2
F = [G(m1)(m2)]/r^2
r^2 = [G(m1)(m2)]/F
By solving I get,
r = 0.00025 cm
But the book answer is 8 cm. Please say which one is right. Here the symbol ^ represents power.

2. May 23, 2006

### Staff: Mentor

Your answer looks OK to me. (G is closer to 6.67 x 10^(-11) N.m^2/kg^2)

3. May 23, 2006

### abercrombiems02

Your work looks correct F = Gm1m2/r^2

In order for the book to be right you must have

Gm1m2/.08^2 = F

This means 6.67e-11*1*1/0.0064 = F

Evaluating gives....

F = 6.67e-11/0.0064 = 1.0422e-8 N

This number is both ugly and way too small for 1kg.wt to be equal to 1.0422e-8 N. I would argue that there is yet another typo in your book. You may want to double check the referencing in the solutions portion of your text.