25. Spider-Man Spider-Man holds the bottom of an elevator with one hand.
With his other hand, he holds a spider cord attached to a 50-kg box of
explosives at the bottom of the cord. Determine the force that the cord
exerts on the box if (a) the elevator is at rest; (b) the elevator accelerates up
at 2.0 m/s2; (c) the upward-moving elevator's speed decreases at a rate of
2.0 m/s2; and (d) the elevator falls freely.