# Kinetic energy problem

1. Nov 13, 2011

### macy192

1. The problem statement, all variables and given/known data
How much energy is required to move this satellite to a circular orbit with a radius of 2.50×104 miles?

I've found the answer to Part A of this problem to be 1.59*10^10, if this helps solve the above^^
(Find the kinetic energy of a 1.80×103 kg satellite in a circular orbit about the Earth, given that the radius of the orbit is 1.40×104 miles.)

2. Relevant equations
v^2=G Me / r
KE = 1/2mv^2
.5*m*v^2=.5*m*(G*mEarth/R)
E = 1/2mv^2 - GMm/r
KE = 1/2mv^2 = 1/2 GMm/r

E = -1/2 GMm/r
dE = E2 - E1 = GMm*(-1/r2 +1/r) = GMm*(r2 -r)/(r*r2)

3. The attempt at a solution
using these formulas have given me three wrong attempts on my homework and i don't know what i'm doing wrong. any help would be very appreciative.

2. Nov 14, 2011

### BruceW

It all looks fine, except, on you final equation, you forgot the 1/2. So it should be:
dE = 0.5 GMm*(r2 - r)/(r*r2)
If you're still getting it wrong after changing this, then maybe you've not converted from miles to meters properly?