A block-and-tackle system is used to lift a load of 20N through a vertical height...

JAMB 1989

A block-and-tackle system is used to lift a load of 20N through a vertical height of 10m. if the efficiency of the system is 40%, how much work is done against friction?

A. 80J
B. 120J
C. 300J
D. 500J

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Correct Answer: Option C

Explanation

Efficiency = \(\frac{output}{input}\) x 100

40 = \(\frac{20\times10}{input}\) x \(\frac{100}{1}\)

input = 500J

work against friction = input - output

= 500 - 200 = 300J

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