Question

efficiency of machines quick check
a rotating space heater used 1,400 joules of energy while heating a room. of that total, 896 joules produced thermal energy, 181 joules produced kinetic energy, some value missing joules produced sound energy. what is the space heater’s efficiency? (1 point)

• 156.25%
• 56.25%
• 25%
• 64%

Explanation:

Step1: Identify useful energy (thermal)

Thermal energy is 896 J (useful for heating).

Step2: Calculate total energy input

Total energy input is 1400 J.

Step3: Apply efficiency formula

Efficiency $= \frac{\text{Useful Energy}}{\text{Total Energy}} \times 100\% = \frac{896}{1400} \times 100\%$
Calculate $\frac{896}{1400} = 0.64$, then $0.64 \times 100\% = 64\%$.

Answer:

64% (the option with 64%)