01 Key Concepts
Work Definition
Work is done when a force causes displacement in the direction of that force: W = F*d*cos(theta), where theta is the angle between the force and displacement.
Positive, Negative, and Zero Work
Work is positive when force and motion align, negative when they oppose (like friction), and zero when force is perpendicular to motion or there's no displacement.
Units of Work
Measured in joules (J), where 1 joule = 1 newton x 1 meter.
Work Done Against Gravity
Lifting an object at constant speed requires work equal to W = m*g*h, where h is the height raised.
Work-Energy Theorem
The net work done on an object equals its change in kinetic energy: W_net = (change in KE).
02 Key Formulas
- W = F*d*cos(theta)
- W (against gravity) = m*g*h
03 Solved Examples
Example 1 A 10 N force pushes a box 5m in the same direction as the force. Find the work done.
- Since force and displacement are aligned, theta=0, cos(0°)=1.
- W = F*d*cos(0°) = 10*5*1.
Answer: 50 J
Example 2 A 20 N force is applied at 60° to the direction of motion, moving an object 4m. Find the work done. (cos(60°)=0.5)
- Apply W = F*d*cos(theta) = 20*4*cos(60°).
- = 80*0.5.
Answer: 40 J
Example 3 Find the work done lifting a 5 kg object 2m straight up (g=10 m/s^2).
- Apply W = m*g*h = 5*10*2.
Answer: 100 J
04 Practice Questions
1A 15 N force pushes an object 3m in the same direction. Find work done.
45 J
2Find the work to lift a 2 kg object 5m (g=10).
100 J
3A force is applied perpendicular to an object's motion. Find the work done.
0 J (cos(90°)=0)
4What is the SI unit of work?
The joule (J)
5What theorem relates net work to change in kinetic energy?
The work-energy theorem
📄 Work — Downloadable Worksheet
10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.