Need help with gravitation conservation of energy problem

[brett812718]

[SOLVED] need help with gravitation conservation of energy problem

Homework Statement

Zero, a hypothetical planet, has a mass of 2.0E23 kg, a radius of 3.0E6 m, and no atmosphere. A 17 kg space probe is to be launched vertically from its surface.
(a) If the probe is launched with an initial kinetic energy of 5.0E7 J, what will be its kinetic energy when it is 4.0E6 m from the center of Zero?

(b) If the probe is to achieve a maximum distance of 8.0E6 m from the center of Zero, with what initial kinetic energy must it be launched from the surface of Zero?

Homework Equations

E=K+U
U=-(GmM/r)

The Attempt at a Solution

E=K initial + U initial
E=5.0E7+(-(6.67E-11)(17)(2.0E23))/3.0E6=-2.56E7
E-U final=K final
-2.56E7--5.67E7=3.11E7J
is this correct?

 

[Dick]

Yes. That's right.

 

[brett812718]

thanks