# Homework Help: Momentom question. But Hard one:O

1. Mar 26, 2009

### remaan

1. The problem statement, all variables and given/known data
The only force acting on a 2 kg object moving along the x axis is shown. If the velocity Vx is 2 m/s at t=0, what is the velociity at t=4 s ?

2. Relevant equations
P= mv

3. The attempt at a solution
Area under the curve is the Impulse, which is Pf - Pi and it's equal to 4
That indicates that p at t=4 - p at t=0 = 4

However, given that v at =0 is 2
By the sub. of the formula we get that P at t=0 is 4 and therefore P at t=4 is 0

Is that Correct ?

2. Mar 26, 2009

### rl.bhat

By the sub. of the formula we get that P at t=0 is 4 and therefore P at t=4 is 0

No. P at t=4 becomes 8

3. Mar 27, 2009

### remaan

Ya, that's ubsolutly right. But what confuses me is that it is a multiple choise ques.

And the choises are
4
5
6
7
2
There isn't any 8 ??

4. Mar 27, 2009

### rl.bhat

You have to post the figure or graph whichever is given in the problem.

5. Mar 27, 2009

### Hannisch

Okay, I might just be very, very confused but:

I = Pf - Pi = mvf - mvi

I/m = vf - vi

vf = vi + ( I/m )

You say vi = 2, I = 4 & m = 2

Then vf = 2 + (4/2) = 4 ?

So yes p(4) = 8, but p=mv & you want to find v..

6. Mar 27, 2009

### remaan

Uha ,

That's right..

Then the velocity becomes 4 ..

Thanks