Efficiency physics problem 84 An internal combustion engine consumes 1 gallon of diesel fuel per hour. It provides a constant 10 hp. One gallon of diesel fuel has potential energy of about 115,000 Btu. Remember that 1 hp × 42.44 = 1 Btu/min. What is the efficiency of the system? **A. 22%** _**Answer_** B. 28% C. 31% D. 35% How I approach this Since 1 gallon an hour is 115,000 then 10hp constant an hour is 424.4 There I use output/input x100. So $424.4/100000 * 100$ I got .42 I am confused in where I went wrong?

First: read _carefully_ the following statement from the problem:

> Remember that $1$ hp × $42.44$ = 1 Btu/${\bf min.}\;$ [Bold-face mine.]

There are $60$ minutes in an hour.

Second: where are you making use of the information regarding potential energy of $\;115,000\;$ BTU?