A girl sits and stands repeatedly for 6 min. Draw a graph to show the variation of potential energy of her body with time.

From the graph shown above, we can take the sitting position of the girl as the position of zero potential energy. Let m be the mass of the girl and h be the position of centre of gravity while standing above the sitting position. The PE while standing is + mgh and while sitting is zero. We can assume that there is no acceleration or deceleration while standing and sitting, this is repeated after every minute.