Motion of particle - Mechanics problem

Question

The problem is:

At time $t=0s$ a particle is moving in a straight line and accelerating uniformly at $2 ms^{-2}$. $5s$ later it stops accelerating, but continues to move at a constant velocity for a further $10s$. At time $t=20s$ the particle has an instantaneous velocity of $-4ms^{-1}$.

Calculate the initial velocity of the particle.

Thanks in advance to everyone for help or hints.

Answer 1

Hint:

First note that if the particle is accelerated for $5s$ , and there are not other acceleration, the velocity of the particle remain constant at any successive time, so the velocity at $10s$ is the same that at $20s$.

Now use the equation for a uniformly accelerated motion: $$ v=v_0+ at $$ with: $v=-4 $, $a =2$ , $t =5$ and find $v_0$.