A student does 100 J of work on the handle of a bicycle pump. The pump does 40 J of work pushing the air into the tire. What is the efficiency of the pump?

1 Answer
Thomas S.
Dec 21, 2015

I calculate 40% efficiency.

Explanation:

The efficiency of a device can be calculated using these steps:

1) Measure the amount of work put in (input);
2) Measure the work that the device puts out (output);
3) Divide the output by the input;
4) Multiply by 100 to get a percentage.

As an equation, this becomes:

#"Efficiency" = ("output")/("input")*100#

The input is the #100J# of work done by the student. The pump's output is #40J#. We can substitute these numbers into the equation and get:

#"Efficiency" = 40/100*100#
#"Efficiency" = 40%#

Efficiency values are always expressed as percentages. This pump is not particularly efficient - less than half the work put in by the student is actually used to pump air! The rest is converted to heat and sound, then lost to the surroundings.

Related questions
Impact of this question
5904 views around the world
You can reuse this answer
Creative Commons License