1. **State the problem:** Determine whether the given scenarios represent examples of work done. 2. **Recall the definition of work:** Work is done when a force causes displacement in the direction of the force. Mathematically, work $W = Fd \cos(\theta)$ where $F$ is force, $d$ is displacement, and $\theta$ is the angle between force and displacement. 3. **Analyze each case:** - a) Teacher applies force to a wall but the wall does not move, so displacement $d=0$. Therefore, $W=0$. **No work done.** - b) Weightlifter lifts a barbell upward, force and displacement are in the same direction. **Work done.** - c) Waiter carries tray at constant speed horizontally, force is vertical (holding up), displacement is horizontal, angle $90^\circ$, so $\cos 90^\circ=0$. **No work done.** - d) Rolling marble hits note card and moves it, force causes displacement. **Work done.** - e) Shot-putter launches shot, force causes displacement. **Work done.** **Final answers:** a) No b) Yes c) No d) Yes e) Yes