A particle is moving such that its position vector varies with time as `vec(r) = (1 - alpha t) t vec(A) `, where `alpha` and `vec(A)` are constant quantities. At `t = 0`, the particle is at a position O. At some later instant `'t_(0)'`, the particle is again at O. Velocity of the particle at the instant `t_(0)` is:

Options

A. `2 vec(A)`
B. `vec(A)`
C. `-vec(A)`
D. `-2 vec(A)`

Answer

C

Explanation

`vec(r) = (1 - alpha t)t vec(A)`
`(d vec(r))/(dt) = (1- 2 alpha t) vec(A)`