Extra · Mechanics · Classes 9–10
Work and power
Objective: To measure the work done and the power developed in climbing stairs.
🧪 Simulation — ideal model
P = W/tWork and power
🧰 Apparatus
- Staircase
- Metre tape (height of steps)
- Stopwatch
- Weighing scale
📐 Formulas and SI units
W = mgh (J)
P = W/t (W); 1 hp = 746 W
💡 Theory
Work done against gravity is W = mgh. Power is the rate of doing work, P = W/t. Running up the same stairs does the same work as walking, but faster, so with more power.
🪜 Procedure
- Measure your mass.
- Measure the height of one step and count the steps.
- Walk up and time it; then run up and time it.
- Calculate W = mgh and P = W/t for each.
- Compare your power with a 60 W bulb.
📋 Observations Simulated values
✅ Result and conclusion
A 50 kg student climbing 3 m in 6 s does 1470 J of work at a power of 245 W.
🔬 In a real lab
Your body also wastes energy as heat; the true chemical power used is several times higher.
⚠️ Safety
Do not race on stairs; hold the rail and walk if the stairs are crowded.
❓ Quick check
1. Walking and running up the same stairs do the same…
2. Unit of power?
3. P = 1000 W for 10 s. Work?
🏋️ Practice
Easy60 kg, 4 m, 8 s. P?
Answer: 294 W
MediumWork lifting 10 kg by 2 m?
Answer: 196 J
ChallengeA 1 kW motor runs 1 hour. Energy?
Answer: 3.6 MJ (1 kWh)