How Does Impulse Affect the Velocity of a Block?

[teenidle]

Homework Statement

A 2kg block, initially moving due east at 6m/s, is acted upon by an impulse having magnitude 4Ns and direction due west. What is the final velocity of the block?
a) 8m/s west
b) 4m/s west
c) 4m/s east
d) 8m/s east

Homework Equations

change in momentum = F*(time interval) = mass*Velocity(final) - mass*velocity(initial)

The Attempt at a Solution

assuming west is the (-) direction
4Ns = (2kg)(-Vf) - (2kg)(6m/s)
2Ns = (-Vf -6m/s)
-8m/s = Vf
so 8m/s west

 

[G01]

You have the right idea, but I think you are making a sign error.

Your relevant equation is correct, so start with that.

Now, the impulse is directed west, so it should be negative based on your sign convention. Also, I don't know why you multiplied v_f by a negative sign in your first line of work. That is changing your answer. What do you get now that you take those sign errors into account?