# Work with a variable force

## Homework Statement

An object is moved from 0 to 9 meters with a force varying according to the function F(x)= 50(5-square root x). What is the work done.

## The Attempt at a Solution

I tried to take the integral and evaluate it from 0 to 9. I get 1350J no matter what I do, which is not correct. The correct answer is given as 1700 J. Any help?

gneill
Mentor

## Homework Statement

An object is moved from 0 to 9 meters with a force varying according to the function F(x)= 50(5-square root x). What is the work done.

## The Attempt at a Solution

I tried to take the integral and evaluate it from 0 to 9. I get 1350J no matter what I do, which is not correct. The correct answer is given as 1700 J. Any help?

It sometimes happens that the given "answer" is not correct. If you show your work in detail then we can see if your method produces a correct result.

I will only say that F(x) is not always positive.

I will only say that F(x) is not always positive.

Yes, but it is positive over the spatial domain in question. Furthermore, since this is a conservative force, the work done from the starting point to the ending point will be independent of the path.

My calculation yields the same number as the OP's.

Yes, but it is positive over the spatial domain in question. Furthermore, since this is a conservative force, the work done from the starting point to the ending point will be independent of the path.

My calculation yields the same number as the OP's.

Yeah you are right..sorry . This must definitely be the most useless hint ever ! :P