Arock is falling off a cliff. the work that gravity performs on the rock is

zero

positive

negative

Positive

Explanation:

Work is defined as the product of displacement of an object produced by the applied force and the component of force along that direction. Let us consider a situation in which the angle between the applied force and the displacement produced by it is at an angle θ. Let the magnitude of displacement be s and that of the applied force be F. Now, we have to find the component of force along the direction of the displacement. For that we have to resolve the force in to two components- one along the direction of displacement and other perpendicular to it. Since the angle between force and displacement is θ, the component of force along the direction of displacement will be Fcosθ and that perpendicular to it will be Fsinθ. Thus, b the definition of work, work done = Fcosθ x s = Fscosθ.

Now, coming to our question, the force here is gravitational force of attraction which is along downward direction. It is given in the question itself that the stone is falling down. Since the displacement and the applied force is along the same direction, angle between them, θ = 0.

Thus, work done = Fscosθ = Fscos0 = Fs (since cos0 =1)

Fs > 0

Thus, the work done is positive