Calculate Kinetic Energy Loss in Collision of 2850 kg & 3200 kg Cars

[snash1057]

kinetic energy loss??

A 2850 kg car moving east at 8.0 m/s collides with a 3200 kg car moving east. The cars stick together and move east as a unit after the collision at a velocity of 4.86 m/s.
(a) Find the velocity of the 3200 kg car before the collision.
2.06 m/s to the east

(b) What is the decrease in kinetic energy during the collision?
?


i have tried KE=1/2mv^2 finding kinetic energy of the cars together before impact and then after


before: 1/2(6050)(10.06^2) = 306140.89 after: 1/2(6050)(4.86^2) = 71449.29

306140.89-71449.29 = 234691.6

but that's not right

 

[gneill]

8.0² + 2.06² ≠ 10.06²

You need to find the separate KE's of the cars before collision and add them in order to find the initial KE.