An electric hoist lifts a cargo of mass m m\,m vertically through a height h h\,h in a time ttt. The electric motor of the hoist is connected to a power supply of potential difference V V\,V and draws a current III. Let g g\,g be the acceleration of free fall.
Which expression gives the efficiency of the hoist?
VItmgh\frac{VIt}{mgh}mghVIt
mghVIt\frac{mgh}{VIt}VItmgh
mhVItg\frac{mh}{VItg}VItgmh
mghtVI\frac{mght}{VI}VImght
