If the particle of mass `m` is moving with constant velocity `v` parallel to x-axis in x-y plane as shown in (figure), Find its angular momentum with respect to origin at any time `t`.

Explanation

At any time t coordinates of the particle will be
`x = vt," "y = b," "z = 0`
and velocity components will be
`v_(x) = v," "v_(y) = 0," "v_(z) = 0`
(The particle is moving parallel to x-axis)
`vec(L) = vec(r) xx vec(p) = m |(hat(i),hat(j),hat(k)),(vt,b,0),(v,0,0)|`
i.e. `vec(L) = m hat(k) [vt xx 0 - vb] = -mvb hat(k)`
Thus, angular momentum has magnitude mvb and is directed along negative z-axis.