Q: A mass m is moving with a constant velocity along a line parallel to the x-axis, away from the origin. Its angular momentum with respect to the origin

(a)Is zero

(b)Remains constant

(c)Goes on increasing

(d)Goes on decreasing

Ans: (b)

Sol: Angular momentum $\large \vec{L} = m(\vec{r}\times \vec{v})$

If θ be the angle between $\vec{r}$ and $\vec{v}$ then ,

$\large L = m v r sin\theta $

$\large L = m v h$ ; Where h = perpendicular distance from X axis

Here , m ,v & h all are constant .