Question

1. an engine is 35% efficient. if it takes in 7,000 j of chemical energy from fuel, how much useful mechanical energy does it produce?

Explanation:

Step1: Define the efficiency formula

Efficiency $\eta=\frac{W_{useful}}{Q_{input}}\times100\%$, where $\eta$ is the efficiency, $W_{useful}$ is the useful mechanical energy output, and $Q_{input}$ is the input chemical - energy.

Step2: Rearrange the formula to solve for $W_{useful}$

We know that $\eta = 35\%=0.35$ and $Q_{input}=7000\ J$. Rearranging the formula gives $W_{useful}=\eta\times Q_{input}$.

Step3: Calculate the useful mechanical energy

$W_{useful}=0.35\times7000\ J = 2450\ J$.

Answer:

$2450\ J$