AP Physics Questions on Work: Exam Prep

📚 Quick Study Guide

• 🏋️‍♀️ Work: Work is done when a force causes a displacement. Mathematically, it's defined as $W = F \cdot d \cdot cos(\theta)$, where $F$ is the force, $d$ is the displacement, and $\theta$ is the angle between the force and displacement vectors.
• ⚡️ Units: The unit of work is the joule (J), where 1 J = 1 N·m.
• ➕ Net Work: The net work done on an object is equal to the change in its kinetic energy: $W_{net} = \Delta KE = \frac{1}{2}mv_f^2 - \frac{1}{2}mv_i^2$. This is known as the work-energy theorem.
• 📐 Angle: The angle $\theta$ is crucial. If the force and displacement are in the same direction, $\theta = 0$ and $cos(0) = 1$. If they are perpendicular, $\theta = 90$ and $cos(90) = 0$, meaning no work is done.
• 🌱 Conservative Forces: For conservative forces (like gravity), the work done is path-independent.
• 🔥 Non-Conservative Forces: For non-conservative forces (like friction), the work done *is* path-dependent.
• 💡 Power: Power is the rate at which work is done: $P = \frac{W}{t}$, where $t$ is time. The unit of power is the watt (W), where 1 W = 1 J/s.

Practice Quiz

1. Question 1: A force of 20 N is applied to an object, moving it 5 meters horizontally. If the force is applied at an angle of 30 degrees to the horizontal, how much work is done?
   1. A) 86.6 J
   2. B) 50 J
   3. C) 100 J
   4. D) 0 J
2. Question 2: A box is pushed across a floor with a force of 10 N. If the work done is 50 J, how far was the box pushed?
   1. A) 5 m
   2. B) 10 m
   3. C) 25 m
   4. D) 500 m
3. Question 3: A 2 kg ball is dropped from a height of 10 m. What is the work done by gravity on the ball as it falls (assume g = 9.8 m/s²)?
   1. A) 196 J
   2. B) 20 J
   3. C) 98 J
   4. D) 0 J
4. Question 4: A 5 kg block is pulled up a frictionless inclined plane that is 3 meters long and elevated 1 meter vertically. How much work is required?
   1. A) 15 J
   2. B) 49 J
   3. C) 147 J
   4. D) 0 J
5. Question 5: A car's engine does 5000 J of work in 10 seconds. What is the power output of the engine?
   1. A) 50 W
   2. B) 500 W
   3. C) 50000 W
   4. D) 10 W
6. Question 6: A constant force of 30 N is used to pull a wagon horizontally a distance of 60 m. How much work is done?
   1. A) 20 J
   2. B) 180 J
   3. C) 1800 J
   4. D) 0 J
7. Question 7: An object moves at a constant speed in a circle. Is work done on the object?
   1. A) Yes, because there is a force acting on the object.
   2. B) No, because the displacement is zero.
   3. C) Yes, because the kinetic energy is changing.
   4. D) No, because the force and displacement are perpendicular.