1. The problem statement, all variables and given/known data A trolley of mass 200 kg moves with velocity of 10 m/s on a friction less track. A child of mass 20 kg runs on the trolley with a sped of 4 m/s relative to the trolley in the direction opposite to the trolley's motion and jumps out of the trolley. What is the final speed of the trolley? 2. Relevant equations La of conservation of momentum 3. The attempt at a solution My reference frame is moving with the velocity of the center of mass. 4*20=200*v v=0.4 Therefore with respect to ground velocity of trolley=10.4 m/sec? Is my answer correct?