a girl on a swing, which is 4 m long, is 2.0 m high at her highest point (all the way back) and 0.5 m above the ground at the closest point (at the bottom). question is how fast is she going and when? im pretty sure her fastest point is at the bottom. to solve it i think you set potential energy equal to kinetic (mgh = 1/2mv^2) and solve for v. but what h do you use? is it 2.0 m or 1.5 m (the difference in heights from top to lowest point)? also, whats the point in mentioning the 4 m long string?