The correct option is D 1s
Lets1 and s2 be the displacements covered by wooden block and bullet respectively.
Given. height of the tower is 100 m
Therefore, s=s1+s2=100 m.
From the second equation of motion,
s=ut+12×at2
Before the collision, in the case of block, initial velocity,u = 0 and the acceleration, a = g (acceleration due to gravity)
s1=12gt2=12×9.8×t2=4.9t2
In the case of bullet, initial velocity, u=100 ms−1 and the acceleration, a = g (acceleration due to gravity)
s2=ut−12gt2
=100t−12×9.8×t2=100t−4.9t2
Substituting the values in equation, s1+s2=100 m, we get,
4.9t2+100t−4.9t2=100
⇒ 100t = 100
⇒ t = 1 s.