1.

A particle of mass m is moving in yz-plane with a uniform velocity v with its trajectory running parallel to +ve y-axis and intersecting z-axis at z = a (Fig. 7.2). The change in its angular momentum about the origin as it bounces elastically from a wall at y = constant is:(a) mva êx (b) 2mva êx (c) ymv êx (d) 2ymv êx

Answer»

The initial velocity is vi = vêy and, after reflection from the wall, the final velocity is vf = -vêy . The trajectory is described as r = yêy + aêz . Hence the change in angular momentum is r x m(vf - vi) = 2mvaêx.

Hence the answer is (b).



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