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## Homework Statement

A 1350kg car travelling at 72km/h collides with a slow-moving car of mass 1650kg, also initially travelling south. After the collision, the velocity of the 2 cars together is 24km/h. Determine the initial velocity at which the second car was travelling.

Given: m1=1350kg.

v

_{i1}= 72km/h=20m/s

v

_{f1}= 24km/h=6.6666666m/s

m2=1650kg

v

_{f2}=6.6666666m/s

## Homework Equations

m1v

_{i1}+m2v

_{i2}=m1v

_{f1}+m2v

_{f2}

## The Attempt at a Solution

1350(20)+1650(x)=1350(6.66666666)+1650(6.66666666)

27000+1650x=9000+11000

27000+1650x=20000

1650x=-7000

x=-4.24242424m/s=-15.2727272km/h

My answer was right except for the negative sign. Does the negative sign mean I did something wrong, because I didn't put negative signs infront of the velocity values in my calculations to indicate direction. What did I do wrong?

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