Physics-
General
Easy

Question

Three objects A comma B and C are kept in a straight line on a frictionless horizontal surface. These have masses m comma blank 2 m and m respectively. The object A moves towards B with a speed 9 blank m divided by s and makes an elastic collision with it. Thereafter, B makes completely inelastic collision with C. All motions occur on the same straight line. Find the final speed (in m divided by s) of the object C

  1. 3 blank m divided by s    
  2. 4 blank m divided by s    
  3. 5 blank m divided by s    
  4. 1 blank m divided by s    

The correct answer is: 4 blank m divided by s



    v subscript 2 end subscript equals fraction numerator 2 m subscript 1 end subscript v subscript 1 end subscript over denominator m subscript 1 end subscript plus m subscript 2 end subscript end fraction equals fraction numerator 2 cross times m cross times 9 over denominator m plus 2 m end fraction equals 6 blank m divided by s
    i. e. After elastic collision B strikes to C with velocity of 6 blank m divided by s. Now collision between B and C is perfectly inelastic

    By the law of conservation of momentum
    2 m cross times 6 plus 0 equals 3 m cross times v subscript s y s end subscript
    rightwards double arrow v subscript s y s end subscript equals 4 blank m divided by s

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