Two massless string of length 5 m hang from the ceiling very near to each other as shown in the figure. Two…

Two massless string of length 5 m hang from the ceiling very near to each other as shown in the figure. Two balls A and B of masses 0.25 kg and 0.5 kg are attached to the string. The ball A is released from rest at a height of 0.45 m as shown in the figure. The collision between two balls is completely elastic. Immediately after the collision, the kinetic energy of the ball B is 1 J. The velocity of ball A just after the collision is

  1. 5 m s-1 to the right
     
  2. 5 m s-1 to the left
  3. 1 m s-1 to the right
     
  4. 1 m s-1 to the left

Solution

KE B = 1 2 m B v B 2

1 = 1 2 × 0 . 5 × v B 2

vB= 2 m s-1

u A = 2 gh

= 2 × 1 0 × 0 . 4 5

= 3 m s-1

From the conservation of linear momentum

0 . 2 5 × 3 + 0 = 0 . 2 5 × v A + 0 . 5 × 2

0 . 7 5 = 0 . 2 5 v A + 1

0 . 2 5 v A = - 0 . 2 5

vA=-1 m s-1

Asked in: Practice

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