NEET-XII-Physics
10: Rotational Mechanics
- #3A particle moves on a straight line with a uniform velocity. Its angular momentum
(a) is always zero
(b) is zero about a point on the straight line
(c) is not zero about a point away from the straight line
(d) about any given point remains constant.digAnsr: b,c,dAns : (b) is zero about a point on the straight line
(c) is not zero about a point away from the straight line
(d) about any given point remains constant
(b) Angular momentum = `` m\left(\stackrel{\to }{r}\times \stackrel{\to }{v}\right)``
If the point is on the straight line, `` \stackrel{\to }{r}\,\mathrm{\,and\,}\stackrel{\mathit{\to }}{\mathit{v}}`` will have the same direction and their cross product will be zero. Hence, angular momentum is zero.
(c) If the point is not on the straight line, `` \stackrel{\to }{r}\,\mathrm{\,and\,}\stackrel{\mathit{\to }}{\mathit{v}}`` will not have the same direction and their cross product will not be zero. Hence, angular momentum is non-zero.
(d) No external torque is applied on the body; therefore, its angular momentum about any given point remains constant.
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