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College Physics (Urone)
Found in: Page 263

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Short Answer

(a) How long can you play tennis on the 800 kJ (about 200 kcal) of energy in a candy bar?

(b) Does this seem like a long time? Discuss why exercise is necessary but may not be sufficient to cause a person to lose weight.

(a) The duration for which you can play tennis is 30.3 min .

(b) Yes, it seems like a long time.

See the step by step solution

Step by Step Solution

Step 1: Power

Power is scalar quantity which is defined how fast the energy is being consumed by the system.


P=Et……………….. (1.1)

Here, E is the amount of energy consumed, and t is the time.

Step 2: The time which you can play tennis


The time can be calculated using equation (1.1).

Rearranging equation (1.1) in order to get an expression for time.


Here, E is the energy of the tennis player E=800 kJ , and P is the power consumed while playing tennis P=440 W .

Putting all known values,

t=800 kJ440 W=800 kJ×1000 J1 kJ440 W=1818.18 sec×1 min60 sec=30.3 min

Therefore, the duration for which you can play tennis is 30.3 min .

Step 3: Exercise is necessary


Yes, this is surprisingly long. Exercise is required to burn more energy than is consumed.

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