A machine of efficiency 80% is used to raise a body of mass 75kg through a vertical height of 3m in 30s. Calculate the power input. (g = 10ms-2)
A
9.4W
B
60.0W
C
75.0W
D
93.8W
Verified Correct Answer: D.
Physical Principles & Numerical Solution
Efficiency = \(\frac{ poweroutput}{powerinput}\)
but power output = \(\frac{ f \times s}{ t}\) = \(\frac{75 \times 10 \times 3}{ 30}\) = 75W
Efficiency = 80%, power output = 75w
then 0.8 = \(\frac{ 75}{powerinput}\)
power input = \(\frac{ 75}{0.8}\) = 93.75W.
Source: Myschool Past Questions Archive (Record #33771)