Question

You do 25 J of work to move a 4 N object 5 meters. What is your efficiency?

Answer 1

0.8 or 80%

Explanation:

Here, the total amount of energy provided by your body is 25 J. However the amount of energy required to move the object (useful energy) through 5 metres is 20 J. The other 5 J will be wasted and converted to other forms like heat in our muscles.

How did I get 20 J?

It's known that:

Work done = Energy transferred

Here, the work done is the product of force and displacement:

`W= f.s`

So:

W= 4 x 5 = 20 J

Now what's the efficiency?

Here it is:

Useful output energy/ Total input energy

So:

`20/25` = 0.8

Or:

`20/25` x 100= 80%