A projectile is launched vertically from the surface of the Moon with an initial speed of 1130 m/s. At what altitude is the projectile's speed three-fourths its initial value?

Answer 1

change in PE=change in KE
PE=1/2 mass(1130^2-(3*1130/4)^2 )

Now PE change is Mass*GMm/(altitude+radiusmoon)
so you have to look up the mass of the moon

Notice the mass divides out.