# Homework Help: Energy between objects

1. Nov 15, 2009

### ryty

1. The problem statement, all variables and given/known data
Two 0.54-k basketballs, each with a radius of 16 cm, are just touching.
A. How much energy is required to change the separation between the centers of the basketballs to 1.0 m?
B. How much energy is required to change the separation between the centers of the basketballs to 14 m?

2. Relevant equations
Im not sure what to use, but its probably obvious

3. The attempt at a solution
None, i dont know where to start

2. Nov 16, 2009

### srmeier

this smells like a universal gravitational potential problem (assuming these balls are not on the surface of the earth), so what is your potential equation?

3. Nov 16, 2009

### ryty

okay, F=G(m1)(m2)/r^2 but if the raduis of the balls are .16 m, do i use that as the radius, or do i double it beause the balls are the same size?

4. Nov 16, 2009

### srmeier

(ignoring the detail with the radius) your expression solves for the force one ball exerts on another. Once you solve for this force, what good is it?

5. Nov 16, 2009

### ryty

im kind of confused, am i using the right equation?

6. Nov 16, 2009

### srmeier

no, use this equation.

$$U=G\frac{m_1m_2}{D}$$

where:
U= potential energy
G= newton's gravity constant
D= distance from either respective centers

7. Nov 16, 2009

### ryty

so it should look like this F=(6.67E-11)(.54)(.54)/.16 ?