Question

An electric motor uses 80 J of energy to lift a mass of 1.8 kg a vertical distance of 2 m. Calculate the efficiency of the machine. Use 10 m/s² for gravity

Answer 1

45%

Step-by-step explanation

Given:

• The energy used by the electric motor, W_in = 80 J

,

• The mass lifted, m = 1.8 kg

,

• The distance the mass is lifted, d = 2 m

Find:

• The efficiency of the machine

The mechanical efficiency of a machine is defined as the quotient between the output work and the input work - usually multiplied by 100 to express it as a percentage,

`efficiency=(W_(out))/(W_(in))\cdot100`

In this case, the work done by the electric motor is 80 J - which is the input work. Let's find how much work is actually required to lift the mass,

`W_(out)=F_g\cdot d=mgd=1.8kg\cdot10m/s^2\cdot2m=36J`

So, the efficiency is,

`efficiency=(36J)/(80J)\cdot100=0.45\cdot100=45\%`

Hence, the efficiency of the machine is 45%.