# Homework Help: Finding Joules of heat for 75% efficient motor at 250hp.

1. Jan 22, 2012

### Moose100

1. The problem statement, all variables and given/known data
Forgive me for any indiscretions my first post.

The problem is to find the Joules of heat per hour produced in a motor that is 75% efficient and requires 0.250hp to run it.

2. Relevant equations

efficiency=1-(Qc/Qh)

3. The attempt at a solution

1. convert hp to Watts; 0.250hp* 746W/hp *75 percent=139W

2. Jan 22, 2012

### Mike Pemulis

Try multiplying by 25 percent instead. 75% efficient means that 25% of the applied work is converted to heat.

3. Jan 22, 2012

### Moose100

I did the problem is that gives me a small number at around 48 the bok says the answer is 168KJ

It's 139 when I multiply by 75%

4. Jan 22, 2012

### Mike Pemulis

I don't know then. Would you mind typing out the problem exactly as it is stated?

5. Jan 22, 2012

### Moose100

No problem.

How many joules of heat per hour are produced in a motor that is 75.0 percent efficient and requires 0.250hp to run it? Ans 168kJ