# Homework Help: I need help with variable forces!

1. Oct 10, 2011

### matt@USA

1. The problem statement, all variables and given/known data
A block is acted on by a force that varies as (1.4*10^4N/m)x for 0<x<.21m , and then remains constant at 2940N for larger x. How much work does the force do on the block in moving it from x= 0 to x= 0.30m? How much work does the force do on the block in moving it from x= 0.10m to x= 0.40m?

2. Relevant equations

3. The attempt at a solution
I am not understanding the question or something. Can someone help me with the equation?

2. Oct 10, 2011

### rock.freak667

Well how would you find the work done with a variable force? (hint: it has an integral in it)

Essentially, the question is telling you that for 0<x<.21 m the force is F = 1.4(104)x and for x>0.21 m, F=2940.

When you get the formula you will need to see what the force will be for the range of x=0 to x=0.4 m. Not that you can split the range as so:

x = 1 to x=4 is the same as x=1 to x=2 + x=2 to x=4.