A certain weight lifting machine of velocity ratio 30 can lift a load of 1500 N with the help of 125 N effort. The efficiency of the machine is _______. 

Concept:

Mechanical Advantage: 

• In a simple machine when the effort(P) balances a load (W), the ration of the load to the effort is called MA.
• \(M.A = \frac{{Load}}{{Effort}} = \frac{W}{P}\)

Velocity Ratio: 

• It is the ratio between the distance moved by the effort to the distance moved by the load.
• \(V.R = \frac{{distance\;moved\;by\;the\;effort\;\left( {{d_P}} \right)}}{{distance\;moved\;by\;the\;load\;\left( {{d_w}} \right)}}\)

Efficiency: 

• It is the ratio of output to input. In a simple mechanism, it is also defined as the ratio of mechanical advantage to the velocity ratio.
• \(\eta = \frac{{Output}}{{Input}} = \frac{{M.A}}{{V.R}}\)

Calculation:

Given:

Load, W = 1500 N, Effort, P = 125 N, V.R = 30

\(M.A = \frac{W}{P} = \frac{1500}{125} = 12\)

\(\eta = \frac{{M.A}}{{V.R}}= \frac{{12}}{{30}}=40\%\)