Initial velocity of car = 0 Acceleration of car = 5 m/s2 Velocity of car at t = 4 s; v = u + at ⇒ v = 0 + 5 × 4 = 20 ms–1 At t = 4 s, A ball is dropped out of a window so velocity of ball at this instant is 20 ms–1 along horizontal. After 2 seconds of motion : Horizontal velocity of ball =20ms−1(∵ax=0) Vertical velocity of ball (vy)=uy+ayt vy=0+10×2=20ms−1(∵ay=g=10m∕s2) So magnitude of velocity of ball (v)=√vx2+vy2=20√2m∕s Acceleration of ball at t=6s is g=10m∕s2 As ball is under free fall.