The total momentum before and after the collision must be conserved.
- Let's start from the end: at this point, both cart and laundry bag are moving together, with a total mass of (m1+m2) and velocity 2.6 m/s. Therefore, the total momentum is
- The momentum must be conserved, so the initial momentum must be equal to this value:
- At the beginning, the cart is stationary, so its momentum is zero. There is only one momentum, the one of the bag, which has a mass of 20 kg and unknwon velocity vi:
- So, using the conservation of momentum we find
and from this, the initial velocity of the laundry bag: