Question

An 84% efficient single pulley is used to lift a 230 kg piano 3.5 m. How much work must be input?

Answer 1

Answer:

35%

Explanation:

win

Answer 2

The amount of work required to lift the 230 kg to a height of 3.5 m at  84% efficiency is 9391.67 J

What is efficiency?

This can be defined as the capacity to achieve a given task with little or no waste. Mathematically, it can be expressed as

Efficiency = (output / input) × 100

How to determine the work output

• Mass (m) = 230 Kg
• Height (h) = 3.5 m
• Acceleration due to gravity (g) = 9.8 m/s²
• Work output =?

Work output = mgh

Work output = 230 × 9.8 × 3.5

Work output = 7889 J

How to determine the work input

• Output = 7889 J
• Efficiency = 84%
• Input =?

Efficiency = (output / input) × 100

84% = 7889 / input

Cross multiply

84% × input = 7889

Divide both side by 84%

Input = 7889 / 84%

Input = 7889 / 0.84

Input = 9391.67 J

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