A 20.0 kg rock is dropped and hits the ground at a speed of 90.0 m/s. What is the rock's gravitational potential energy before it was dropped?

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Answer 1 · 2018-03-14T21:59:21

#GPE = 81000J or 81kJ#

ground level = #KE_0 , GPE_0#
*before it was dropped = #KE_h, GPE_h#

#GPE_h + KE_h = GPE_0 + KE_0#

#KE_h = 0 and GPH_0 = 0#

So

#GPE_h = KE_0#

#GPE_h = 1/2m(v)^2#

#GPE_h = 1/2 * 20 * (90)^2#

#GPE_h = 81000J = 81kJ#