The blades of a fan are turned by an electric motor. In one second, 300 J of energy is transferred electrically from the mains supply. 85 J is wasted due to friction and sound.
Calculate the efficiency of the motor.
Step 1: List the known quantities
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- Total energy input = 300 J
- Total wasted energy = 85 J
Step 2: State the equation
Step 3: Determine total energy output
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- Due to the conservation of energy:
total energy input = total energy output
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- Therefore, total energy output = 300 J
Step 4: Calculate the useful energy output
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- Due to conservation of energy
Total energy output = useful energy output + wasted energy
Useful energy output = total energy output − wasted energy
Useful energy output = 300 − 85
Useful energy output = 215 J
Step 5: Substitute these values into the efficiency equation