text: what is the mechanical efficiency of the lifting system and motor if...? an electric motor rated at 100w is used to raise a mass of 50kg through 5m in 50 secs.   could you also show a method for how to work this out please? thanks put simply, efficiency equals the power you receive divided by the power you put in. you'll need these 4 basic equations. power = work / time work = force * distance force = mass * acceleration efficiency = output/input (in %)  the motor is rated at 100w, so that is the power you put in. to lift 50kg, you need to overcome gravity. in this case, mass = 50kg, gravitational acceleration = 9.81 m/s. from here you can calculate the force required. then you can calculate the work done, and then the power. this is the power you receive. from here, you can calculate the efficiency.  try to work it out on your own. you'll learn more.