Power
Two pumps lift the same water into the same tank. One takes 10 seconds (10 s). One takes 30 seconds (30 s).
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Step 1 of 4
- Both pumps start at time t = 0 s, empty.
- Pump A finishes at t = 10 s. It ran at 60 W (watts).
- Pump B finishes at t = 30 s. It ran at 20 W (watts).
- Same work, different power.
The pump that takes 10 seconds has more power. It does the same work in less time.
Rule
Power is the rate of doing work. Power = work ÷ time. The unit is the watt.
- Power — the work done in one second.
- Watt (W) — one joule of work each second.
Both pumps lift the same water into the same tank. So both do the same work, 600 J. Pump A: power = 600 ÷ 10 = 60 W. Pump B: power = 600 ÷ 30 = 20 W.
A crane lifts 100 kg by 3 m in 6 s. Take g = 10 m/s². The lifting force is 100 × 10 = 1000 N. Work = 1000 × 3 = 3000 J. Power = 3000 ÷ 6 = 500 W.