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
Verified Correct Answer: C.
Physical Principles & Numerical Solution
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
Source: Myschool Past Questions Archive (Record #28321)