# Forces with universal gravity

1. Homework Statement

A bowling ball (mass = 7.2 kg, radius = 0.10 m) and a billiard ball (mass = 0.48 kg, radius = 0.028 m) may each be treated as uniform spheres. What is the magnitude of the maximum gravitational force that each can exert on the other?
N

2. Homework Equations

F=G((m1*m2)/r^2)

g being gravitaional constant

3. The Attempt at a Solution

G((7.2*.48)/(.128))=1.801e-9

Related Introductory Physics Homework Help News on Phys.org
Where is r^2?

i have solved it by

((7.2*.48)/(.128*2))*G

the only thing i didnt understand was where the objects relative to each other so i presumed they were touching.

fluidistic
Gold Member
Take a look at the formula $$F=\frac{Gm_1m_2}{r^2}$$. $$G$$ is a constant and so are $$m_1$$ and $$m_2$$. Now we ask ourselves a question : " when will $$F$$ reach a maximum when $$r$$ varies?". It's obvious that more $$r$$ is little more $$F$$ is greater. So $$F$$ reaches a maximum when $$r$$ reaches its minimum. And what is the minimum of $$r$$? It's simply the sum of the radius of the 2 balls, as you did. So it will be $$0.128\text{ m}$$.
Take care about what you wrote in the denominator of
((7.2*.48)/(.128*2))*G
, I think you forgot that $$r$$ was squared and not multiplied by $$2$$. Otherwise everything's good.