Question

A 40.0-kg student climbs up a ladder to the roof of a building. The gravitational potential energy of the student at this point is 2.00 x 103 J. How high is the student above the ground?

Answer 1

By definition, the gravitational potential energy is

$$U = mgh$$

where $m = 40kg$ is the mass of the object, $h$ is its height above the ground, and $g = 9.81m/s^2$ is the gravitational acceleration. Since $U = 2\times 10^3J$, the height is

$$h = \dfrac{U}{mg} = \dfrac{2\times 10^3J}{40kg\cdot 9.81m/s^2} \approx 5.1m$$

Answer. 5.1 m.