Question

A rock is lying at the top of a 2 m high cliff and it possesses a potential energy of 80 J. What is the mass of the rock?

Answer 1

By the definition of the potential energy, we have:

$$PE=mgh,$$ $$m=\dfrac{PE}{gh}=\dfrac{80\ J}{9.8\ \dfrac{m}{s^2}\cdot2\ m}=4.08\ kg.$$