- #1

Student-

- 5

- 0

## Homework Statement

Air passes over an electrical heater at a steady rate of 2500cm^3 per second. The inlet temperature of the air is 20^oC ( 20 degrees celcius ) and the steady outlet temperature is 40^0C ( 40 degrees celcius)

a) What heat is absorbed by air passing over the heater in 2 hours

b) Obtain an estimate for the power rating of the heater

Density of air ( 1.2 kgcm-3)

Specific heat capacity of air : 1000 J-1Kg-1K-1

## Homework Equations

So I think that I should use the equation Q=mcΔθ

## The Attempt at a Solution

Here's what I did :

2500cm^3=2500g=2.5kg

Since 2.5kg is heated every second then 2hrs of heating would heat 2.5x7200 = 18,000kg of air.

ΔθOutlet-Inlet temperature = 40-20 = 20 degree celcius change in temperature,

Specific Heat capacity of air : 1000 Jkg-1K-1

Q=mxcxΔθ

= 18000x1000x20

=3.6x10^8

Which is wrong because the answer at the back of the book had 4.32x10^5. I've tried, but I really need some help :) Thanks