# Impulse-Momentum Theorem Q.

1. Jun 30, 2005

### Eiano

I have this problem that says a 3 kg object has a velocity of 7.00m/s j (vertical, right?). Then a total of 12.0Ni (horizontal) acts on it for 5 seconds. What is the objects final velocity.

I know that the equation is Ft=mvf-mvi

I could just plug everything in, but what's bothering me is the fat that the mass has an vertical velocity and the force is acting on it horizontally. Am I reading this wrong or is this the case?

If so, how do I go avout finding what I need to plug in.

My work:

Ft=mvf-mvi
(12N)(5s)=(5)(vf)-(5)(7)... then solve for vf, but that seems too easy.

2. Jun 30, 2005

### Nylex

The object is moving in the vertical direction with that velocity, yes and then the force acts on it for 5 seconds. So yeah, that is the case.

You still use $\vec{F}t = m(\vec{v_{f}} - \vec{v_{i}})[/tex] and solve for [itex]\vec{v_{f}}$, but writing the force and inital velocity in terms of vectors and not just their magnitudes.

Last edited: Jun 30, 2005
3. Jun 30, 2005

### OlderDan

The motion in the x direction is independent of the motion in the y direction. Since there is no y-directed force, the y-velocity will be unchanged. In you last equation, you should only have x-directed quantities. You substituted the wrong number for mass, and you have the wrong initial velocity.

After you get the final x-velocity, you need to add it to the y-velocity by vector addition.

OOPs- scooped again

4. Jun 30, 2005

### Eiano

ohhh i didn't mean to put in 5 as the mass :)
so i have to find the initial velocity first? it's not just 7 huh.....
then find the final V and doo Vector addition,

ok thank you all very much!!!