   Chapter 12, Problem 73AP

Chapter
Section
Textbook Problem

Suppose you spend 30.0 minutes on a stair-climbing machine, climbing at a rate of 90.0 steps per minute, with each step 8.00 inches high. If you weigh 150. lb and the machine reports dial 600. kcal have been burned at the end of the workout, what efficiency is the machine using in obtaining this result? If your actual efficiency is 0.18, how many kcal did you actually bum?

To determine
What efficiency is the machine using and how many Kcal will be burned actually.

Explanation

Section1:

To determine: the efficiency that the machine is using.

Answer: The efficiency that the machine is using is 14.5%

Explanation:

Given Info:

The energy burned at the end of the work out is 600kcal

The time spend on the stair climbing machine is 30min .

The height of each step is 8in/step .

The climbing rate is 90.0step/min

The mass of the person is 150lb .

Formula to calculate the efficiency is,

e=Weng|Qh|=mg(Δh)|Qh|

• Δh is the change in height
• |Qh| is the energy input by heat
• m is the mass of the you
• g is acceleration due to gravity.

Substitute 150lb for m, (90.0step/min)(8in/step) for Δh and 600kcal for |Qh| to find the efficiency,

e=[(150lb)(4.45N1lb)][(90.0step/min)(30.0min)(8.0in/step)(2.54×102m1in)](600kcal)(4186J1kcal)=3

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