Ablue train of mass 50 kg moves at 4 m/s toward a green train of 30 kg initially at rest. the trains collide. after the collision the green train moves with a speed of 3 m/s. what is the final momentum of the blue and green train combined?
a. 90 kgm/s
b. 110 kgm/s
c. 50 kgm/s
d. 200 kgm/s

Consider a small frictionless puck perched at the top of a fixed sphere of radius r. if the puck is given a tiny nudge so that it begins to slide down, through what vertical height will it descend before it leaves the surface of the sphere? [hint: use conservation of energy to find the puck's speed as a func e conservation of energy to find the puck's speed as a function of its height at what value of this normal force does the puck leave the sphere? ] here on the puck.