Finding Mechanical Energy without knowing Efficiency

[jennyskywalker]

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?

 

[SteamKing]

How much energy must the man expend to lift his mass up the mountain?

 

[jennyskywalker]

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!

 

[jennyskywalker]

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!

 

[SteamKing]

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.