# Common velocity after truck starts pulling a car

## Homework Statement

Truck is connected to a car with a rope of given length. The truck starts accelerating with a given acceleration and at some moment starts pulling the car. What is their common velocity just after the car starts moving?

## Homework Equations

I know how to calculate the velocity of the truck just before the car starts moving. Than I use the conservation of momentum or the conservation of energy.

## The Attempt at a Solution

I get different results when I use momentum and when I use kinetic energy. Which one is conserved, which is not and why?

Orodruin
Staff Emeritus