How much water would be required to absorb this heat?

[Intrusionv2]

Homework Statement

The United States generates about 5.7 x 10^16 J of electric energy a day. This energy is equivalent to work, since it can be converted into work with almost 100% efficiency by an electric motor.

(a) If this energy is generated by power plants with an average efficiency of 0.32, how much heat is dumped into the environment each day?

Answer --> 1.21e+17 J

(b) How much water would be required to absorb this heat if the water temperature is not to increase more than 2.7° C?

Answer --> 1.07e+13 kg.

The Attempt at a Solution

I don't see how it is possible to pump out more heat into the environment than work generated, especially at 0.32 efficiency. Can someone help me with this problem please? Thanks

 

[rl.bhat]

a) Efficiency = work output/work input.
In the problem, work output and efficiency is given. Find work input.
heat is dumped into the environment each day = work input - work output.
b) Q = m*c*change in temperature.

 

[Andrew Mason]

I don't see how it is possible to pump out more heat into the environment than work generated, especially at 0.32 efficiency. Can someone help me with this problem please? Thanks

Following on what rl.bhat has said, the work is generated from heat engines. The heat engines only convert a fraction (.32) of the heat flow into work. The rest is expelled as waste heat.

AM

 

[gneill]

Following on what rl.bhat has said, the work is generated from heat engines. The heat engines only convert a fraction (.32) of the heat flow into work. The rest is expelled as waste heat.

AM

One might argue that virtually *all* of the generated power is eventually expelled as waste heat; mostly it is used to heat things, illuminate things, and do repetitive tasks in a friction-filled environment. Elevators go down as well as up!