Question

Ignoring air resistance, a ball dropped from rest at altitude 250km strikes the ground with (a) 1500m/s (b) 2200m/s (c) 2800m/s
I already know that is 2200m/s but don't understand why???

Answer 1

From Vf^2 = Vo^2 + 2gh

Vf^2 = 0 + 2(9.8)250,000 making
Vf = 2213m/s

or

From h = Vo(t) = g(t^2)/2

250,000 = 9.8t^2/2 making t = 225.87sec.

and

Vf = Vo + gt

Vf = 0 + 9.8(225.87) = 2213m/s