Question

How much potential energy is lost by a 5Kg object to kinetic energy due a decrease in height of 4.5 m.

Answer 1

potential energy =mgh
=5×10×4.5
=225j
potential energy losed by law of conservation of mass.
=1/2 (total p.e)
=1/2 (225)
=112.5j

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Answer 2

potential energy at h = 4.5 m

potential energy = -mgh = -5 × 10 × 4.5
= - 225 joule

potential energy at h=0
potential energy = -mgh = 0

change in potential energy = potential energy at h = 0 - potential energy at h = 4.5 m

= 0 - ( -225) joule = 225 joule

hence, decrease in potential energy = - change in potential energy = -225 joule