Work, Energy & Power – TS EAMCET Physics Notes
(Beginner‑friendly, everyday language, short sentences, tiny examples)
1. Work
| What it is | Everyday analogy | Formula | Unit |
|---|---|---|---|
| Work = “how hard you push something to make it move” | Pushing a heavy box across the floor | W = Force × Distance × cos θ | Joule (J) |
Key points
- Force – the push or pull you apply.
- Distance – how far the box moves while you push.
- θ – angle between the force and the direction of motion.
If you push straight forward, θ = 0°, cos θ = 1. - If θ = 90° (force perpendicular to motion), no work is done (e.g., holding a heavy box while it slides).
Tiny example
You push a box with 10 N force for 5 m straight forward.
W = 10 N × 5 m × cos 0° = 50 J.
The box has 50 J of work done on it.
2. Energy
Energy is the ability to do work. Two common types:
| Type | Where it comes from | Everyday analogy | Formula | Unit |
|---|---|---|---|---|
| Kinetic Energy (KE) | Motion | A running ball | KE = ½ × mass × velocity² | J |
| Potential Energy (PE) | Position or shape | A ball on a hill | PE = mass × g × height | J |
- g ≈ 9.8 m/s² (gravity on Earth).
Work–Energy Principle
The work done on an object equals its change in kinetic energy.
W = ΔKE = KE_final – KE_initial
Tiny example
A 2 kg ball is thrown upward 3 m.
PE = 2 kg × 9.8 m/s² × 3 m = 58.8 J.
At the top its speed is 0 m/s, so all the energy is potential.
3. Power
Power = “how fast work is done”
| What it is | Everyday analogy | Formula | Unit |
|---|---|---|---|
| Power | How quickly you lift a box | P = Work ÷ Time | Watt (W) |
1 W = 1 J/s.
Tiny example
You lift a 10 kg bag 2 m in 4 s.
Work = mass × g × height = 10 kg × 9.8 m/s² × 2 m = 196 J.
Power = 196 J ÷ 4 s = 49 W.
4. Quick Formula Sheet
| Symbol | What it means | Formula |
|---|---|---|
| W | Work | F × d × cos θ |
| KE | Kinetic Energy | ½ m v² |
| PE | Potential Energy | m g h |
| ΔKE | Change in Kinetic Energy | KE_f – KE_i |
| P | Power | W ÷ t |
5. Practice Problems (with answers)
| # | Question | Answer |
|---|---|---|
| 1 | A 5 kg box is pushed 4 m with a 20 N force at 0°. How much work? | 80 J |
| 2 | A 3 kg ball is thrown straight up 5 m. Its PE at the top? | 147 J |
| 3 | A 2 kg car speeds up from 0 to 10 m/s. Its KE change? | 100 J |
| 4 | You do 200 J of work in 10 s. What is the power? | 20 W |
6. Quick Tips for Exams
- Read the problem carefully – find what is being asked: work, energy, or power.
- Identify given values – force, distance, mass, height, time, velocity.
- Pick the right formula – use the table above.
- Check units – force in N, distance in m, time in s → work in J, power in W.
- Remember cos θ – if not given, assume force is in the direction of motion (θ = 0).
Final Thought
Think of work as the “push” you give, energy as the “power‑up” that lets something move, and power as the “speed” of giving that push. Master these three ideas and you’ll ace the Work‑Energy‑Power section of TS EAMCET!