Question

The position of a particle is given by : and momentum $\vec { P } = ( 3 \hat { i } + 4 \hat { j } - 2 \hat { k } )$. The angular momentum is perpendicular to

• A. X-axis
• B. Y-axis
• C. Z-axis
• D. Line at equal angles to all the three axes

Answer 1

Answer: (A)

X-axis

Answer 2

$\vec { L } = \vec { r } \times \vec { p } =$ $= 0 \hat { i } - \hat { j } - 2 \hat { k } = - \hat { j } - 2 \hat { k }$

and the X- axis is given by $i + 0 \hat { j } + 0 \hat { k }$

Dot product of these two vectors is zero i.e. angular momentum is perpendicular to X-axis.