When a mass is rotating in a plane about a fixed point, its angular momentum is directed along (a) a line perpendicular to the plane of rotation (b) the line making an angle of 45° to the plane of rotation (c) the radius (d) the tangent to the orbit

Answer: (a). L = r × p; both r and p lie in the plane of rotation. So L is perpendicular to that plane: answer (a).

When a mass is rotating in a plane about a fixed point, its angular… | NEET 2012 (AIPMT, Prelims)

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Angular Momentum & its Conservation

When a mass is rotating in a plane about a fixed point, its angular momentum is directed along

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Answer: (a)

$\vec L = \vec r \times \vec p$ ; both $\vec r$ and $\vec p$ lie in the plane of rotation.
So $\vec L$ is perpendicular to that plane: answer (a).