Calculate Magnitude of Work from 0.22 Lawnmower Engine in 1 Second

[bulbasaur88]

A lawnmower engine with an efficiency of 0.22 rejects 9900 J of heat every second. What is the magnitude of the work that the engine does in one second?

e = 0.22
Q_c = 9900 J/s

e = W/Q_h
Q_h = Q_c + W

e = W / Q_c + W
0.22 = W / 9900 + W
0.22(9900 + W) = W
2178 + 0.22W = W
W = 2792.31 J/s?

I checked my answer on cramster.com but they have something different, but I believe my answer to be right. Can anybody verify if I am doing this correctly or not? Thank you.

 

[Andrew Mason]

A lawnmower engine with an efficiency of 0.22 rejects 9900 J of heat every second. What is the magnitude of the work that the engine does in one second?

e = 0.22
Q_c = 9900 J/s

e = W/Q_h
Q_h = Q_c + W

e = W / Q_c + W
0.22 = W / 9900 + W
0.22(9900 + W) = W
2178 + 0.22W = W
W = 2792.31 J/s?

I checked my answer on cramster.com but they have something different, but I believe my answer to be right. Can anybody verify if I am doing this correctly or not? Thank you.

Your answer should be expressed in the correct number of significant figures. You may want to simplify your answer algebraically before plugging in the numbers:

Qh = Qc/(1-e)

W = eQh = e(Qc/(1-e))

Also, you have to put your answer for W in the correct units. J/s is a unit of power.

AM