The efficiency of a machine is 80%.calculate,the amount of energy needed by the machine to do work of 150joules.

To calculate the amount of energy needed by the machine to do work, we need to consider the efficiency of the machine. Efficiency is defined as the ratio of useful work output to the total energy input.

Efficiency = (Useful work output / Total energy input) * 100%

In this case, the efficiency of the machine is given as 80% or 0.80.

So, we can rearrange the formula to solve for the total energy input:

Total energy input = (Useful work output / Efficiency)

Given that the useful work output is 150 joules, and the efficiency is 80%, we can substitute these values into the equation:

Total energy input = (150 joules / 0.80)

Calculating this, we have:

Total energy input = 187.5 joules

Therefore, the machine needs an input of 187.5 joules of energy to do a work output of 150 joules.