Question

A ball is released from a roof 40 m high. Calculate the velocity of the ball when it just reaches the ground.​

Answer 1

Answer:

Given that,

Height = 40 m

Time t =2 sec

We know that,

v=u+gt

v=0+9.8×2

v=19.6m/s

The speed of stone is 19.6 m/s

Now, the speed with which the stone strikes the ground

v

2

=u

2

+2gs

v

2

=0+2×9.8×40

v

2

=784

v=28m/s

Hence, the speed with which the stone strikes the ground is 28 m/s

Answer 2

Answer:

height=40 cm ,time ? , g=9.8 ,u=0

now using second equation of motion

s=ut +1/2gt²

40=0+1/2*9.8*t²

40*2/9.8=t²

8.16=t²

t=√8.16

t=2.85sec

Now using first equation of motion

v=u+gt

v=0+9.8*2.85

v=28.05 m/s