A ball is thrown horizontally from a height of 20 m. It hits the ground with a velocity three times its initial velocity. The initial velocity of ball is
Given that,
Initial speed = u
Height = 20 m
This speed will remain constant throughout the journey.
Horizontal component of velocity when it hits the ground is
vx=u
if vy be the vertical component of velocity when it hits the ground then,
v2y=2gh
v2y=2×9.8×20
v2y=392m2/s2
Now, final speed of object
=√v2x+v2y
=√u+392
Now, according to question
√u+392=3u
9u2=u2+392
8u2=392
u2=49
u=7m/s
Hence, the final velocity is 7 m/s