# Efficiency question.

1. Oct 20, 2008

### usagi101

A student performs an experiment in which an electric motor is used to lift a 200g weight through 2m, thus increasing its potential energy 4J. from measurements of the rate at which the weight is lifted the efficiency of the motor is to be determined. Two different voltages were used and the current was measured.
a) in the first experiment at 6V a current of 0.25A was measured and the weight took 5s to rise the 2m what was the efficiency of the motor.

Ok. well in our class we havent even learnt about effiency so i have no idea how to approach, although our teacher said we dont need to know this type of Questions for exams or anything i would still like to know how to do it. Could anyone please explain thanks!

2. Oct 20, 2008

### tiny-tim

Hi usagi101!

Efficiency just has its usual English meaning … amount of energy obtained divided by amount of energy supplied.

The energy obtained is calculated from the height and the mass.

The energy supplied is calculated from the volts the amps and the time.

Have a go!