Work Energy And Power

A spring scale is adjusted to read zero. Particles of mass 1 g fall on the pan of the scale and collide elastically and they rebound upward with the same speed. If the height of fall of panicles is 2 m and their rate of collision is 100 particles per second, then the scale reading in grams will be

A smooth sphere of mass m moving with velocity u directly collides elastically with another sphere of mass M at rest. After collision their final velocities are V and v respectively. The value of v is