Correct Answer - Option 3 : 2
The correct answer is 2.
Given,
Mass (m) = 2 tonnes = \(2\times10^3Kg\).
Height (h) = 60 meters.
Acceleration due to gravity (g) = 10 m/s.
Time (t) = 20 minutes = \(20\times60\ seconds\)
Efficiency = 50% = \({1 \over2}\)
\(Power(Output) = {Work \over Time}\) ...1)
\(Work= m\times g\times h\) ...2)
Substitute 2) in 1)
\(Output \ Power = {2\times10^3\times10\times60 \over 20\times60}\)
\(Output\ Power=10^3 watts\)
\(Efficiency = {Output \ Power \over Input\ Power}\)
\({1 \over 2}={10^3\over Input\ Power}\)
\(\therefore\;Input\ Power=2\times10^3 watts = 2\ kW\).
