Question

A particle of mass `m` is moving along the line `y=b,z=0` with constnat speed `v`. State whether the angular momentum of particle about origin is increasing. Decreasing or constant.

Answer 1

Angular moment of particle
`|L|=mvrsin theta`
`=mvr_(bot)=mvb`

`:. |L|=` constant as `m,v and b` all are constants.
Direction of `r xx v` also remains the same. Therefore, angular momentum of particle about origin remains constant with due course of time
Note : In this problem , `|r|` is increasing `theta` is decreasing but `r sin theta`. i.e., b remains constant. Hence, the angular momentum remains constant.