Question

If the efficiency of a machine is 80% and it consumes 500 W of power, what is the useful output power?

• A. 400 W
• B. 420 W
• C. 450 W
• D. 480 W

Hint:

Efficiency problems require careful unit consistency; always convert percentages to decimals for calculations.

Answer 1

The Correct Option is A

Step 1: Understand efficiency
Efficiency = (Useful output power / Input power) $\times$ 100.
Given efficiency = 80%, input power = 500 W.
Step 2: Set up the formula
Efficiency = $\frac{\text{Output power}}{\text{Input power}} \times 100$.
$\Rightarrow 80 = \frac{\text{Output power}}{500} \times 100$.
Step 3: Solve for output power
$\Rightarrow \text{Output power} = \frac{80 \times 500}{100}$.
$\Rightarrow \text{Output power} = 400$ W.