Thermodynamics - Change in Temp

[Jess_18033152]

Homework Statement

A 77.1 kg hiker uses 191 kcal hr-1 (converted to 222.133 J.s ?) of energy whilst hiking. Assuming that 20% of this energy goes into useful work and the other 80% is converted to heat within the body, calculate the temperature change, in units of Kelvin (K), of the hiker's body during a 2.9 hour (converted to 10440s) long hike.

Assume that none of this generated heat is transferred to the environment during the hike. The average specific heat capacity of a human body is 0.83 kcal kg-1 oC-1. (converted to 3475.04 J/kg/K ?)

The answer needs to be given in Kelvin,

Homework Equations

Q = mc(change in temperature)

The Attempt at a Solution

Change in temp = Q/mc = 222.133/(77.1 x 3475.04)
=8.29 x 10^-4 K
Answer is wrong, I feel like I need to be using the time given also...

 

[Andrew Mason]

Homework Statement

A 77.1 kg hiker uses 191 kcal hr-1 (converted to 222.133 J.s ?) of energy whilst hiking. Assuming that 20% of this energy goes into useful work and the other 80% is converted to heat within the body, calculate the temperature change, in units of Kelvin (K), of the hiker's body during a 2.9 hour (converted to 10440s) long hike.

Assume that none of this generated heat is transferred to the environment during the hike. The average specific heat capacity of a human body is 0.83 kcal kg-1 oC-1. (converted to 3475.04 J/kg/K ?)

The answer needs to be given in Kelvin,

Homework Equations

Q = mc(change in temperature)

The Attempt at a Solution

Change in temp = Q/mc = 222.133/(77.1 x 3475.04)
=8.29 x 10^-4 K
Answer is wrong, I feel like I need to be using the time given also...

Q is the total heat flow generated by the hiker over the 2.9 hour hike. How much energy does he use in 2.9 hours? How much of that results in heat flow into the body?

AM

 

[Nathanael]

Hi jess, you must be in Kevin’s class! https://www.physicsforums.com/threads/heat-question.945804/

Indeed, you need to use the time. Note that 191 kcal/hr is 222 J/s (not J.s)

Q is supposed to be a quantity of energy but for Q you’ve plugged in 222 J/s which is a measure of power not energy.