Inelastic car collision, answers aren't matching up

Homework Statement

Car A, having a mass of 1.30 x 10+3kg is traveling at 60.0 km/h due east when it collides with car B, having a mass of mass 1.70 x 10+3kg traveling at 40.0 km/h due west. If the collision is totally inelastic, find the final velocity of car B.
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Homework Equations

I'm using the equation
m1v⃗ 1+m2v⃗ 2=(m1+m2)vf

The Attempt at a Solution

I'm getting 146,000 = (3000)Vf which I'm then dividing to get a velocity of 48.66. But the answer key is telling me 3.33km/h due east. I haven't taken physics in years and am super rusty so any help would be much appreciated.

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gneill
Mentor
Hi BananasAreCool, Welcome to Physics Forums.

Did you take into account the fact that the cars are traveling in opposite directions?

Hi BananasAreCool, Welcome to Physics Forums.

Did you take into account the fact that the cars are traveling in opposite directions?
That's what I was thinking was the problem, what is the equation for them moving in opposite directions?

That's what I was thinking was the problem, what is the equation for them moving in opposite directions?
I was just able to figure it out, I had to subtract instead of add the two so instead of getting 146,000 I got 10,000, which divided by 3,000 equals to 3.33km/h.

gneill
Mentor
I was just able to figure it out, I had to subtract instead of add the two so instead of getting 146,000 I got 10,000, which divided by 3,000 equals to 3.33km/h.
Yup. Well done.