IIT JEE 2009 Physics Paper2 Code 1 Solutions

12.    A steady current I goes through a wire loop PQR having shape of a right angle triangle with PQ = 3x, PR = 4x and QR = 5x. If the magnitude of the magnetic field at P due to this loop is k , find the value of k.

Sol.   7

                        

        We have ,

        B = (μ₀ I)/(48π * 12x/5)  [cos 53^o + cos 37^o] = 7 (μ₀ I)/48πx

        k = 7

13.    A light inextensible string that goes over a smooth fixed pulley as shown in the figure connects two blocks of masses 0.36 kg and 0.72 kg. Taking g = 10 m/s², find the work done (in joules) by the string on the block of mass 0.36 kg during the first second after the system is released from rest.

                                

Sol.   8

                                 

         Applying Newton's 2^nd law,

        2mg - T - 2ma

        T - mg = ma

       => a = g/3

        T = 4mg/3

        W = Tension .Displacement = T . 1/2 at² = 8 Joules

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