Question

A trophy sits on top of a shelf 2.30 m above the floor. If the trophy has a potential energy of 90 J, its mass is __________ kg.

Answer 1

$$E_p=mgh$$

$$m=\frac{E_p}{gh}=\rm\frac{90\: J}{9.8\: N/kg*2.30\: m}=4.0\:kg$$