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**[SOLVED] Two carts with masses of 8.0 kg and 1.8 kg, respectively, move on a friction**

## Homework Statement

Two carts with masses of 8.0 kg and 1.8 kg, respectively, move on a frictionless track with velocities of 8.0 m/s and 3.5 m/s. The carts stick together after colliding head-on. Find the final speed.

## Homework Equations

m1v1+m2v2 = v (m1 + m2)

v_final = (m1*v1 + m2*v2)/(m1+m2)

## The Attempt at a Solution

(8*8)+(1.8*3.5)=70.3

so

70.3=(8+1.8)V

which is then 70.3=9.8V

V=7.17

but it says i'm doing it wrong. (webassign problem)

please show me how i did it wrong?? or whats wrong?