Question

select the equation that shows that the efficiency of a machine that has an input of 100 j and an output of 70 j is 0.70. efficiency = \frac{useful energy output}{total energy input}=\frac{70 j + 100 j}{100 j}=0.70 efficiency = \frac{useful energy output}{total energy input}=\frac{70 j + 100 j}{70 j}=0.70 efficiency = \frac{useful energy output}{total energy input}=\frac{100 j}{70 j}=0.70 efficiency = \frac{useful energy output}{total energy input}=\frac{70 j}{100 j}=0.70

Explanation:

Step1: Recall efficiency formula

Efficiency = $\frac{\text{useful energy output}}{\text{total energy input}}$

Step2: Identify values

Useful energy output = 70 J, total energy input = 100 J

Step3: Calculate efficiency

Efficiency = $\frac{70\ J}{100\ J}=0.70$

Answer:

Efficiency = $\frac{\text{useful energy output}}{\text{total energy input}}=\frac{70\ J}{100\ J}=0.70$ (the last option)