Question 77 of 81 An electric drill transfers 200 J of energy into a useful kinetic energy store II wastefully transfers 92. of energy to the thermal store of the drill and the surroundings What is the efficiency of this drill? Give your answer as a percentoge to 2 significant figures Enter your answer as a number

Question

Question 77 of 81 An electric drill transfers 200 J of energy into a useful kinetic energy store II wastefully transfers 92. of energy to the thermal store of the drill and the surroundings What is the efficiency of this drill? Give your answer as a percentoge to 2 significant figures Enter your answer as a number

Answer 1

200/292 *100 =68.5%

Answer 2

Efficiency in energy transfer is defined as useful output energy divided by total input energy. The output energy reflected in the problem is “200J” since it is transferred to a useful kinetic store. The energy wastefully transferred to the thermal store, “92J”, is also effectually inputted energy, in addition to the useful kinetic energy. Therefore, the total energy transferred is the sum of useful kinetic energy and energy transferred to thermal store, which equals 200J + 92J = 292J. Thus, the efficiency of this drill can then be calculated by dividing useful output energy by total input energy, and represented as a percentage to two significant figures.

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