Key relationship
W = mgh; Paverage = W/τ; constant-speed lifting: P = Fv = mgv.
Physics · Class 11
Equal work, different power
Work is energy transferred. Power is the rate of that transfer. Both lifts raise the same mass through the same height and therefore do equal work against gravity. The lift with shorter duration needs greater average power. At constant speed the force is mg, giving P = mgv.
Open the interactive experiment →Doing the same work faster needs greater power.
வேலை என்பது மாற்றப்படும் ஆற்றல்; திறன் என்பது ஆற்றல் மாற்றத்தின் வீதம். ஒரே சுமையை ஒரே உயரத்திற்கு குறைந்த நேரத்தில் தூக்க அதிக திறன் தேவை.
Key notes, relationships and model limits
Remember
Work is energy transferred. Power is the rate of that transfer. Both lifts raise the same mass through the same height and therefore do equal work against gravity. The lift with shorter duration needs greater average power. At constant speed the force is mg, giving P = mgv.
Common trap
A faster lift does not necessarily do more total work when mass and height are unchanged.
Model limits
Equal loads move upward at constant speed over the same height. Start/stop acceleration intervals and motor inefficiency are neglected. Power readouts describe the active lifting interval.
What you will learn
Distinguish work from power and connect W/t with F·v.
Try the experiment
Play the two-duration preset. Compare final heights, equal work and different power. Then set durations equal.
Think of it this way
Two water pumps can fill identical tanks, while the faster pump transfers energy at a greater rate.
Worked example
A 20 kg load raised 3 m gains 588.6 J. In 3 s the power is 196.2 W; in 6 s it is 98.1 W.
Why this matters
Power ratings help match a machine to a required rate of energy transfer.
Before you start
Vector components · velocity · SI units
Check your understanding
Two lifts do the same work; A takes half B’s time. A’s average power is…
- Half B’s
- Twice B’s
- Equal to B’s
Read the explanation
P = W/t; halving the time doubles average power.
Course connection: CBSE XI Chapter 5; NEET/Main Unit 4; JEE Advanced Mechanics. Apply each exam’s stated assumptions.