Question

supposed to vacuum cleaner uses 120 J of electrical energy. If 45 J used to pull air into a vacuum cleaner, how efficient is the vacuum cleaner?

Answer 1

Answer:

The efficiency of the vacuum cleaner is 37.5%

Explanation:

The efficiency of a machine can be calculated as

Efficiency = (work output ÷ work input) × 100%

Work output (according to the question) is 45J of electrical energy

work input (according to the question) is 120J of electrical energy

Efficiency = (45 ÷ 120) × 100

Efficency = 37.5 %

The efficiency of the vacuum cleaner is 37.5%

NOTE: Vacuum cleaner is a machine and a machine can not be 100% efficient

Answer 2

we know that

Power efficiency is defined as the ratio of the output power divided by the input power:

so

$efficiency =\frac{ Power\ out}{Power\ in} *100$

in this problem

$Power\ out=45J\\ Power\ in=120J$

Substitute in the formula above

$efficiency =\frac{ 45}{120} *100$

$efficiency =37.5$%

therefore

the answer is

the efficient is $37.5$%