Work done in physics

Question

A crane at a construction site slowly lowers a concrete pillar hanging from a vertical steel cable. The pillar descends with constant velocity. For each of these following statements, mark if they are true or false.

T F a) The work done on the pillar by the gravity is negative.

T F b) The magnitude of the work done by the tension of the cable is less than the the magnitude of the work done by gravity.

T F c) The net work done on the pillar is zero

T F d) The work done on the pillar by tension is zero.

Answer 1

For this situation you should use the relationship:

W = ΔE, or the work performed is equal to a change in Energy.

Since the the velocity is constant, only the change in Gravitational Potential Energy (mgΔh) is what is at play here.

The direction of the force (mg) and the Δh must be taken into account.

For a) they are both negative.

b) is only asking about the "magnitude", so only the number is important.

c) and d), is the Gravitational Potential Energy changing?