Question

work only occurs when which of the following happens? *
1 point
the force is in the same direction as motion. whether it is in motion does not matter.
any time there is kinetic energy.
the force is in the same direction as motion and there is motion.
an object is in motion.

Explanation:

To determine when work occurs, recall the physics definition: Work ($W$) is done when a force ($F$) causes displacement ($d$) in the direction of the force, given by $W = Fd\cos\theta$, where $\theta$ is the angle between force and displacement. If $\theta = 0^\circ$ (force same as motion) and displacement ($d>0$, i.e., motion) occurs, work is done.

• First option: Wrong, as motion (displacement) is required.
• Second option: Wrong, kinetic energy exists in motion, but work needs force in direction of motion (e.g., an object moving at constant velocity with no net force does no work, but has KE).
• Third option: Correct, matches $W = Fd\cos0^\circ = Fd$ (when $\theta = 0$ and $d

eq0$).

• Fourth option: Wrong, motion alone isn’t enough (e.g., uniform motion with no force in direction of motion does no work).

Answer:

C. The force is in the same direction as motion and there is motion. (Note: Assuming option labels are A, B, C, D with C being "The force is in the same direction as motion and there is motion" based on the options provided.)