Question

A body of mass m is moving with constant velocity v along a line parallel to x-axis. The angular momentum with respect to origin.

• A. Remains constant
• B. Is zero
• C. Goes on decreasing
• D. Goes on increasing

Answer 1

The correct option is A Remains constant

Consider initial position of particle is
$r=x\hat{i}+y\hat{j}$
As the particle moves parallel to x-axis with constant velocity.
So, $r=v\hat{i}=$ constant
The angular momentum of particle is given by
$L=r\times p=v\times mv$
$=m(x\hat{i}+y\hat{j})\times \left(v\hat{i}\right)=mvy(\hat{j}\times \hat{i})$
$L=-mvy\hat{k}$.
Since, v and y are constants, so L is also constant.