Why the angular momentum perpendicular to the axis ${L_ \bot }$ in a rotational motion about a fixed axis ? 

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

$A$ uniform rod is fixed to a rotating turntable so that its lower end is on the axis of the turntable and it makes an angle of $20^o$ to the vertical. (The rod is thus rotating with uniform angular velocity about a vertical axis passing through one end.) If the turntable is rotating clockwise as seen from above. What is the direction of the rod's angular momentum vector (calculated about its lower end)?

A $bob$ of mass $m$ attached to an inextensible string of length $l$ is suspended from a vertical support. The $bob$ rotates in a horizontal circle with an angular speed $\omega\,  rad/s$ about the vertical. About the point of suspension

The position vector of $1\,kg$ object is $\overrightarrow{ r }=(3 \hat{ i }-\hat{ j })\,m$ and its velocity $\overrightarrow{ v }=(3 \hat{ j }+ k )\,ms ^{-1}$. The magnitude of its angular momentum is $\sqrt{ x } Nm$ where $x$ is

Explain Angular momentum of a particle and show that it is the moment of linear momentum about the reference point.