Is the work done by the following forces considered in Exercise 9.1 positive, negative, or zero? In each case the system is the object on which the force is exerted.

(a) The force exerted by a hand compressing a spring, 

\((b)\) the force exerted by Earth on a ball thrown upward,

(c) the force exerted by the ground on you at the instant you jump upward, 

\((d)\) the force exerted by the floor of an elevator on you as the elevator moves downward at constant speed.

Data from Exercise 9.1

For which of the following forces is the force displacement nonzero: 

\((a)\) the force exerted by a hand compressing a spring,

(b) the force exerted by Earth on a ball thrown upward,

(c) the force exerted by the ground on you at the instant you jump upward, 

\((d)\) the force exerted by the floor of an elevator on you as the elevator moves downward at constant speed?