NEET Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति NEET PYQ-Work Energy Power and Collision

A force of 250 N is required to lift a 75 kg mass through a pulley system. In order to lift the mass through 3 m, the rope has to be pulled through 12 m. The efficiency of system is: [AIPMT 2001]

A) 50%

B) 75%

C) 33%

D) 90%

Correct Answer: B

Solution :

Efficiency of the system is

\[\eta =\frac{\text{output}\,\,\text{work}}{\text{input}\,\,\text{work}}\]

Input work \[=Fs=250\times 12\]

Output work \[=mgh=75\times 10\times 3\]

So, \[\eta =\frac{75\times 10\times 3}{250\times 12}=0.75=75%\]