A projectile is shot straight up from the earth's surface at a speed of 1.20 x 104 km/hr. How high does it go?

Answer 1

you can work this from kinemetics, but l like energy...

initial KE= change in PE
1/2 m vi^2=GMe*m (1/(re+1.2E7m) - 1/re)

but GMe/re^2= 9.8m/s^2
so 1/2 vi^2=9.8 re (1/(re+h) - 1/re)
now, change vi to m/s, look up radius of earth re in meters, and solve for h