Question

A simple pendulum of length has a bob of mass. As the Bob moves from position P to R. The work done against gravity is ___________

Answer 1

The gravitational field is conservative. This means, that its work done from one point to another depends only on the vertical distance between these points, not on the path they are connected with.

Thus the work against gravity:

$$W = mgh$$

where $m$ is the mass of the bob, $g \approx 9.81m/s^2$ is the gravitational acceleration, and $h$ is the vertical distance between $P$ and $R$. The work will be negative if $P$ is higher than $R$ and positive otherwise.

Answer. mgh.