# Speed with work energy theorem

1. Oct 8, 2015

### PAstudent

1. The problem statement, all variables and given/known data

3. The attempt at a solution

I was wondering if I did something wrong for the 50m. I did the same process of finding the area under the line. I'm assuming it's possible to get the same speed since the net work is the same.

2. Oct 9, 2015

### haruspex

Yes, it will be the same as for 20.

3. Oct 9, 2015

### PAstudent

The 50m cannot be checked because it has a variable force from 20-50 and no longer a constant acceleration

4. Oct 9, 2015

### haruspex

Not sure what you mean. Do you mean it cannot be checked analytically? It can. You would need to express the variable force as a function of x and integrate with respect to x to find the work done.

5. Oct 9, 2015

### PAstudent

It says explain why Newton's second law and the constant acceleration kinematics equations cannot be used to check for the 50m

6. Oct 9, 2015

### haruspex

Yes, but that says using "constant acceleration" kinematics. As you say, it is not constant acceleration. But it can be checked analytically by using kinematics that cope with variable acceleration because the nature of that variation is known exactly.