A weightlifter curls a 32 kg bar, raising it each time a distance of 0.50 m. How many times must he repeat this exercise to burn off the energy in one slice of pizza? Assume 25% efficiency.

Explanation:

Average energy contained by  a slice of pizza is 860 J  .

energy used in lifting 32 kg bar by .50 m = mgh

= 32 x 9.8 x .5 = 156.8 J

efficiency is 25 % , so energy used up = .75 x 156.8 = 117.6 J

So number of times exercise to be repeated to burn off energy of a slice of pizza

= 860 / 117.6

= 7.3 or 7 times .

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