The efficiency of a lifting machine will be maximum, when the mechanical advantage 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.

\(\eta = \frac{{Output}}{{Input}} = \frac{{M.A}}{{V.R}}\)

from the above, it is clear that The efficiency of a lifting machine will be maximum when the mechanical advantage of the machine is maximum.