If a boy drops a ball from a window and the ball takes 3s to hit the ground, what is its velocity the second before it hits the ground? Take gravity as 10m/s^2 . (Neglect air resistance)

From given conditions we observe that,

ball takes 3s to hit the ground, then one second before it hits the ground is two seconds, so time given here is 2s

we also find that ,

initial velocity =u= 0 m/s

final velocity =v= ? m/s

g = acceleration due to gravity = 10m/s²

time interval= t = 2 s

Calculate the velocity of the ball at 2 s,

v = u + gt

v = 0 + (10  × 2 ) = 20 m/s