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**Question:**A car of mass 1500kg collides head-on with a truck of mass 9000kg. After the collision, the wreckage is at rest. The speed of the car just before the collision was 30m/s. What was the speed of the truck just before the collision?

Relevant Equation(s):

Relevant Equation(s):

m1v1+m2v2 = m1v1'+m2v2' (?)

**My Attempt:**

(1500kg)(30m/s)+(9000kg)( ___m/s) = (1500kg)(0m/s)+(9000kg)( 0m/s)

(1500kg)(30m/s)+(9000kg)( ___m/s) = 0

(45000 kg*m/s)+(9000kg)(___m/s) = 0

**Problem:**It's 1 in the morning and I'm not understanding what I'm doing wrong. Am I using the right equation? Do I need to set up west and east on the x-axis??