At a particular instant velocity and acceleration of a particle are `(-hat(i)+hat(j)+2hat(k))m//s` and `(3hat(i)-hat(j)+hat(k))m//s^(2)` respectively at the given instant particle's speed is `:`

Options

A. increasing
B. decreasing
C. constant
D. can't say

Answer

B

Explanation

`vec(v)=-hat(i)+hat(j)+2 hat(k)`
`vec(a)=3 hat(i)-hat(j)+hat(k)`
`vec(a).vec(v)=-3-1+2 lt 0`
hence `theta gt 90^(@)` between and so speed is decreasing
`vec(a).vec(v) = -3 -1 + 2 lt 0`.