It is well known that a raindrop falls under the influence of the downward gravitational force and the opposing resistive force. The latter is known to be proportional to the speed of the drop but is otherwise undetermined. Consider a drop of mass `1.00g` falling from a height `1.00km`. It hits the ground with a speed of `50.0 ms^(-1)`.
What is the work done by the unknown resistive force?

Explanation

From the work-energy theorem `triangleK= W_(g)+W_(r )`
where `W_(r )` is the work done by the resistive force on the raindrop. Thus
`W_(r )= triangleK- W_(g)`
`=1.25-10= -8.75 J`
is negative.