Impulse Question -- A car changing speed and direction

[mailmas]

Homework Statement

Cart travels with a mass of 100kg in the 25m/s in the X-Direction and then 20m/s in the Y-Direction. What is the impulse?

Homework Equations

I = m*change in velocity

The Attempt at a Solution

I = 100(20 (j) - 25(i))
I = (2000 (j) - 2500(j)) kg* m/s
Is this correct?

 

[Chandra Prayaga]

Why do you doubt it?

 

[rude man]

The Attempt at a Solution

I = 100(20 (j) - 25(i))[/B]

Why the minus sign?

 

[Chandra Prayaga]

What do you think "change in velocity" means?

 

[haruspex]

Why the minus sign?

Because these are before and after velocities.

and then

 

[rude man]

Because these are before and after velocities.

Oh yes? I interpreted the problem as starting from zero velocity and ending with 25 i + 20 j. The change is just that.

 

[Chandra Prayaga]

There is no "beginning" or "starting from zero" in the statement of this problem. The statement says that it has a velocity of 25 i which then becomes 20 j. In the final situation, the car is traveling with a velocity of 20 m/s in the y direction. It is not traveling with a velocity of 25 i + 20 j.

 

[haruspex]

Oh yes? I interpreted the problem as starting from zero velocity and ending with 25 i + 20 j. The change is just that.

You are still ignoring the "and then". These are sequential circumstances.