1. The problem statement, all variables and given/known data Ok so my teacher used this example in class, he had this flat wheeled cart rolling on the floor. The object was to release a bucket of sand on top of the flat cart to see if the cart would slow down or accelerate. Easily, all of us the students predicted that the cart would slow down, which was the correct awnser because momentum is velocity times mass. And mass does matter, however when we inversed the experiment, starting the bucket of sand on top of the cart and removing it halfway of its pattern to see wether the cart would accelerate or stay the same ? Many of us said it would accelerate... however it stayed the same.... how ? 2. Relevant equations velocity times mass = momentum 3. The attempt at a solution Well I was thinking that maybe, mass can be canceled out since weight is a force... and I also though that velocity cannot be canceled out? I'm really not sure on this one... hopefully I can get some hints. Thank you for reading and for your time.