Question

Please explain and guide,, DON'T tell me the answer. A bowling ball (mass ball (mass 0.38 kg, radius 7.2 kg, radius 0.11 m) and a billiard 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?

I'm looking for someone to guide me to the answer not to tell me the answer.

This is what I know and have:

Fg = G Mm/r^2.

G= 6.674x10^-11.

My question is how to find the distance?

Answer 1

I'm thinking that adding both radius an then squaring them might lead me to the right answer. I want to make sure that I'm following the logic correctly.

Answer 2

and if so , can anyone tell my why that approach would be correct?

Answer 3

They will touch when their centers are as far apart as the sum of their radii.
That distance is to be used to calculate the maximum gravitational attraction.

Answer 4

In your formula the value for r represents the distance between the two centres of mass

As you (and Douglas) say above - the maximum force will be when the distance is minimum - i.e. the balls are touching.

So the distance between the centres IS the sum of the 2 radii

Use this sum in the formula to calculate the force (I think maybe you have not given ALL the information in the question? you need the mass and radius of each ball - maybe it is just a typo...)

Answer 5

Mr. Nood, Douglas, just to make sure i understand I drew it, is my drawing correct? Mr. Nood, both masses were given, it was a typo. Fgmax force is when two objects are touching each other, otherwise it would just be Fg, meaning the distance between them plus the each object's radius correct ?

Answer 6

Looks correct to me.

The distance should of course be measured through the point of contact - and is hence r1 + r2

Answer 7

Understood, thank you very much for the explanation. =) I"m a physicist in the making , I'm trying to understand everything =)