Three carts are moving on a frictionless horizontal track as shown in the figure. The 4.00 kg cart is moving to the right with a speed of 7.0 m/s, the 10.0 kg cart is also moving to the right with a speed of 6.0 m/s while the 3.00 kg cart moves to the left with a speed of 5 m/s. Find the final speed of the carts when they are all stuck together. Hint: The order at which the carts stick together does not matter. Can you see why?

Question

Been stuck on this for a while, i've used my inelastic equation but i just dont get the correct answer.

Answer 1

add the momentums, set them equal to the final momentum.
mass1*V1+mass2*V2+mass3*V3=(mass1+mass2+mass3)Vfinal
make certain you use right as + speed, left as - speed.

Answer 2

Thank you!!! I didn't make the velocity negative for the cart going left! That was all i was doing wrong. I'm kicking myself.