Question

An object does free fall motion. It hits the ground after 4 seconds. Calculate the velocity of the object after 3 seconds and before it hits the ground. What can be the height it is thrown?​

Answer 1

Given that,

Height h=39.2m

Velocity u=19.6m/s

Now, from equation of motion

Case (I) when stone dropped from the tower fall freely

s

1

=ut+

2

1

gt

2

s

1

=0+

2

1

gt

2

....(I)

Now, case (II) when stone projected upward

s

1

=19.6t−

2

1

gt

2

....(II)

Now, total distance

s=s

1

+s

2

s=

2

1

gt

2

+19.6t−

2

1

gt

2

39.2=19.6t

t=2sec

Now, put the value of t in equation (I)

s

1

=

2

1

×9.8×4

s

1

=19.6m

Now, the distance is

s=s

1

+s

2

s

2

=39.2−19.6

s

2

=19.6m

Hence, Both stones meet from ground in air at the distance of 19.6 m in 2 sec