A ball is thrown vertically upwards with a speed of 24 m/s from a roof that is at a height of 12 m from the ground.
As the ball rises up, there is a gravitational force of attraction that accelerates the ball at 9.8 m/s^2 in a direction vertically downwards. Due to the gravitational attraction, the upward velocity of the ball decreases and it comes to a halt at the highest point. As the ball starts to move down its velocity in the downwards direction increases. By the time the ball returns to the level of the roof it is traveling at 24 m/s in the downward direction.
The increase in its velocity while it travels the 12 m from the roof to the ground given by v^2 = 2*9.8*12
=> v = 15.33 m/s
The total velocity of the ball when it strikes the ground is 24 + 15.33 = 39.33 m/s.
The velocity of the ball when it strikes the ground is 39.33 m/s in a vertically downward direction.