Motion in a Plane

$\text{At }t=20\ \mathrm{s}$velocity of truck,$v=0+5 \times 20=100\ \mathrm{m}/\mathrm{s}$At 20 sec a ball is dropped from the truck, so velocity of ball will be same as truck.Velocity of truck at $x$-direction $=100\ \mathrm{m}/\mathrm{s}$ and in $y$-direction $=0$.$\therefore$ Velocity of ball $v_x=100\ \mathrm{m}/\mathrm{s},\ v_y=0$Now ball will show projectile motion where vertically downward acceleration $g=10\ \mathrm{m}/\mathrm{s}$ act on the ball.As horizontally no acceleration acting on the ball so horizontal velocity $100\ \mathrm{m}/\mathrm{s}$ will remain unchanged.Velocity of the ball when it reach the ground along y-direction after 1 sec.$v_y=0-10 \times 1$ $\Rightarrow v_y=-10\ \mathrm{m}/\mathrm{s}$$\therefore$ Velocity of ball $(\overrightarrow{v})=100\hat{i}-10\hat{j}$