# Physics

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Suppose you spend 30.0 minutes on a stair-climbing machine, climbing at a rate of 75 steps per minute, with each step 8.00 inches high. If you weigh 150 lb and the machine reports that 690 kcal have been burned at the end of the workout, what efficiency is the machine using in obtaining this result?
I know the answer to the first part is

10.4%

but i'm not sure how to find this second part...
If your actual efficiency is 0.20, how many kcal did you really burn?
___________kcal

• Physics -

To have an efficiency of 20% and to have done the same amount of work, you need to have burned fewer kcal, by a ratio of 10.4/20. That makes 359 kcal

• Physics -

How did you get the first part?

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