The Motion

An object A is kept fixed at the point $x=3 \text { m}$ and $y=1.25 \text{ m}$ on a plank P raised above the ground. At time $t=0$ it starts moving along $+x$ direction with an acceleration of $1.5 ms^{-2}$ . At that instant a stone is projected with a speed of $\vec{u}$ a stationary person on ground observes the stone hits the object work an angle of 45 degree during downward motion. Find $\vec{u}$ and time taken to hit. Take $g = 10 \text{ m/s}^2$ .