Force, work, power and energy

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Force, work, power and energy

Post by rajathadri on Sun Jul 04, 2010 10:31 am

Consider the following situations and try to answer the questions.

I Shamsher takes 5 minutes while Shashank takes 6 minutes to do 50 chin-ups. Who is more powerful if their weights are the same?


Anuj takes 10 seconds while Aruna takes 8 seconds to climb a 40-step staircase. Can you say that Aruna is more powerful than Anuj if both have the same weight?

III Amit takes 5 seconds to lift a bucket of water from a well while Ravinder takes only 3 seconds to do so. Who is more powerful?

In each of the above examples, there is a comparison between the times taken by two different persons to do a certain amount of work, i.e., the rate of work done by one person is compared with that of the other. We define this ‘rate of work done’ as the ‘power’ of the person.

Power is defined as the rate of work done.

Power (P) is given by the ratio of work done (W) and the time taken (t) to do that work, i.e.,

Power =


This relation shows that for a given work, power is inversely proportional to the time taken.

In case I, the time taken by Shamsher is less than that taken by Shashank for the same work (with both having the same weight). Hence, the power of Shamsher is greater than that of Shashank. Hence, Shamsher is more powerful than Shashank.

In case II, Anuj takes more time to climb the stairs than Aruna. Hence, Aruna is more powerful than Anuj.

Finally, in case III, Amit takes more time to lift a bucket of water from the well than Ravinder. Hence, Ravinder has more powerful than Amit.

Whenever work is done, an equal amount of energy is consumed. Hence, we define power as

Power =

The SI unit of power is watt (W), in honour of the physicist James Watt.

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