4. Two football players with mass 75 kg and 100 kg run directly toward each other with speeds of 6 m/s and 8 m/s respectively. If they grab each other when they collide and have an inelastic collision, the final velocity would be:
A) -2 m/s B) 2 m/s C) 7.1 m/s D) -7.1 m/s
5. A dart of mass Md is launched straight upward toward a block of mass Mb that hangs at rest from a string, as shown in Figure 1. Immediately before the dart collides with the block, the dart has a speed Vo. The dart then collides with and sticks to the block, and the dart-block system travels upward to a height H before the system comes to rest, as shown in Figure 2. What is the magnitude of the change in momentum of the dart-block system immediately before the collision to the instant when the system comes to rest?
A. Zero B. mdvo C. (md +mb)vo D. ½ (md +mb)vo
Md = mass of dart, mb = mass of block, vo = velocity of dart before impact.