Question

A particle is moving along a straight line parallel to $x$ -axis with constant velocity. Its angular momentum about the origin

• A. decreases with time
• B. increases with time
• C. remains constant
• D. is zero

Answer 1

Answer: (C)

Suppose the particle of mass $m$ is moving with speed
$v$ parallel to $x$ axis as shown in figure, then
at any time $t$, coordinates of $P$ will be
$x=vt,y=b$ and $z=0$
while components of velocity will be
$v_x=v,v_y=0$ and $v_z=0$
(as it is moving parallel to $x$ -axis)


l.e., angular momentum has magnitude $mvb$ and is directed
along negative $z$ -axis, i.e., angular momentum remains constant.