A 60% efficient engine is used to haul 200 kg steel beams up to the ninth floor.How much energy needs to be supplied to the engine to lift the beams from the second floor 20 m below?

Question

Quizplus · Accepted Answer

To calculate the energy needed, first find the work done to lift the beams, which is given by the formula $W = mgh$, where $m$ is the mass in kg, $g$ is the acceleration due to gravity (approximately $9.8 \, \text{m/s}^2$), and $h$ is the height in meters. Here, $m = 200 \, \text{kg}$, $g = 9.8 \, \text{m/s}^2$, and $h = 20 \, \text{m}$, so $W = 200 \times 9.8 \times 20 = 39,200 \, \text{J}$. Since the engine is 60% efficient, the energy supplied $E$ is given by $E = \frac{W}{\text{efficiency}}$, so $E = \frac{39,200}{0.6} = 65,333.33 \, \text{J}$, which rounds to $65,400 \, \text{J}$, making option B the correct answer.

A 60% Efficient Engine Is Used to Haul 200 Kg