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Most Important Selected Qs for JEE AdvancedPhysicsCenter of Mass, Momentum and Collision

A person throws a ball (A) vertically upwards with 40 ~m / sec . After 4 sec , he throws another identical ball (B) upwards with same speed. If the collision between balls is head-on perfectly elastic, the speed of ball (A) just after collision is

Options

  1. A0
  2. B10 ~m / sec
  3. C20 ~m / sec
  4. D40 ~m / sec

Correct answer

C. 20 ~m / sec

Step-by-step solution

aligned & v^2=u^2+2 gh 0^2= (40^2 )-2(10)( h ) & h =80 ~m aligned where h is maximum height reached by ball Av=u-g t t=4 sec t^ = 80 u_A+u_B =2 sec u _ A ^ = gt t ^ =20 ~m / s u _ B ^ =40-2 10=20 ~m / s Thus the speed of each ball gets interchanged (for equal mass & elastic collision)

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