# A projectile is fired vertically from the Earth's surface with an initial speed of 11.4 km/s.?

How can I do this? I've tried this like five times and still don't get it. I think I'm supposed to use KE + PE = (KE + PE)final

then

(1/2)mv^2 - GMm/R = 0 - GmM/(R+h)

I tried working this out so many times but I still can't get the right answer for h

Update:

A projectile is fired vertically from the Earth's surface with an initial speed of 11.4 km/s. Neglecting air drag, how far (in meters) above the surface of the Earth will it go?

### 1 Answer

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- NCSLv 73 years agoFavorite Answer
What do you get when you evaluate the LHS? Since v = 11.4 km/s is suspiciously close to the escape velocity, you should get 0 J. So for the RHS to be 0 J, h needs to approach infinity.

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