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

s1 =ut+ 2/1gt²

s1 =0+2/1gt²....(I)

Now, case (II) when stone projected upward

s1 =19.6t−2/1gt2....(II)

Now, total distance

s=s1+s2

s=2/1gt²+19.6t−2/1gt²

39.2=19.6t

t=2sec

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

s1= 2/1 × 9.8 × 4

s1=19.6m

Now, the distance is

s=s1+s2

s² =39.2−19.6

s²=19.6m

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