Physics-
General
Easy

Question

A light inextensible string that goes over a smooth fixed pulley as shown in the figure connects two blocks of masses 0.36 blank k gand 0.72 blank k g. Taking g equals 10 blank m divided by s to the power of 2 end exponent, find the work done (in joules) by the string on the block of mass 0.36 blank k g during the first second after the system is released from rest

  1. 6 blank J o u l e    
  2. 5 blank J o u l e    
  3. 8 blank J o u l e    
  4. 2 blank J o u l e    

The correct answer is: 8 blank J o u l e


    In the given condition tension in the string

    T equals fraction numerator 2 m subscript 1 end subscript m subscript 2 end subscript over denominator m subscript 1 end subscript plus m subscript 2 end subscript end fraction g equals fraction numerator 2 cross times 0.36 cross times 0.72 over denominator 1.08 end fraction cross times 10
    T equals 4.8 blank N
    And acceleration of each block
    a equals open parentheses fraction numerator m subscript 2 end subscript minus m subscript 1 end subscript over denominator m subscript 1 end subscript plus m subscript 2 end subscript end fraction close parentheses g equals open parentheses fraction numerator 0.72 minus 0.36 over denominator 0.72 plus 0.36 end fraction close parentheses g equals fraction numerator 10 over denominator 3 end fraction blank m divided by s to the power of 2 end exponent
    Let ‘S’ is the distance covered by block of mass 0.36 blank k g in first sec
    S equals u t plus fraction numerator 1 over denominator 2 end fraction blank a t to the power of 2 end exponent rightwards double arrow S equals 0 plus fraction numerator 1 over denominator 2 end fraction open parentheses fraction numerator 10 over denominator 3 end fraction close parentheses cross times 1 to the power of 2 end exponent equals fraction numerator 10 over denominator 6 end fraction blank m e t e r
    therefore Work done by the string W equals T S equals 4.8 cross times fraction numerator 10 over denominator 6 end fraction
    rightwards double arrow W equals 8 blank J o u l e

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