Finding Mechanical Energy without knowing Efficiency

AI Thread Summary
To find the Mechanical Energy expended during a 72-minute hike up a 400-meter mountain, the total energy consumed is calculated as 727.2 kcal based on a consumption rate of 10.1 kcal/min. However, this total includes energy lost as heat, and the challenge lies in determining the efficiency of the energy conversion. The relevant equation for Mechanical Energy (ME) is ME = (Efficiency x Eout)/100, where Eout is the total energy expended. The potential energy (PE) gained from climbing can be calculated using the formula PE = mgh, which represents the energy used to lift the man's mass against gravity. Ultimately, understanding the distinction between total energy expended and useful Mechanical Energy is crucial for solving the problem.
jennyskywalker
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Homework Statement


A 65 kg man goes for a 72 minute hike up a mountain that is 400.0 metres in vertical height. The energy consumption rate for this climb is 10.1 kcal/min. What is the Mechanical Energy (useful work energy) expended for this hike? (in kcal)


Homework Equations


ME= (Efficiency x Eout)/100

The Attempt at a Solution


10.1 x 72 = 727.2 (Therefore Eout=727.2) But I don't know the efficiency! So how do I figure this out?
 
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How much energy must the man expend to lift his mass up the mountain?
 
SteamKing said:
How much energy must the man expend to lift his mass up the mountain?

727.2 kcal? But that is the total energy expended, including heat energy. ME=(efficiency x 727.2)/100. That's all I know!
 
I asked on another forum, and they said ME= mgh, but according to my teacher, PE (potential energy)=mgh, and I'm looking for Mechanical energy!
 
energy is energy.

The man expended so many kcal thru his metabolism while walking up the hill. That you have calculated.

However, in moving his mass up the hill, a certain portion of this energy was consumed in moving his mass up the hill against gravity. This energy is equal to the change in gravitational potential from the bottom of the hill to the top.
 

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