Question

catches the student just before reaching the ground ? [Assume that the superman's acceleration is the
In the above question, what must be the maximum height of the skyscraper so that even superman can
A student determined to test the law of gravity for himself walks off a sky scraper 320 m high with a
stopwatch in hand and starts his free fall (zero initial velocity). 5 second later, superman arrives at the
scene and dives off the roof to save the student. What must be superman's initial velocity in order that he
(C) v = u + at
(D) v = u
of any freely falling body.] (g = 10 m/s2)
(A) 98 m/s
275
(B) m/s
3
(C)
187
m/s
2
(D) It is not possible
save him.
(A) 65 m
(B) 85 m
(C) 125 m
(D) 145 m
The variation of velocity of a partirlo
houn in the fiqura Tho​

Answer 1

Answer:

The initial velocity of superman is 91.66 m/s. Then, So, the total time taken for the free fall of student from the sky scrapper is 8 s. According to the question, superman arrives after 5 s, so he has (8-5)=3 s to save the student from reaching the ground.

Explanation:

. . .. .. . . .

Answer 2

Option C => 125m

Assuming superman can move at infinite speed, he would be able to save the student unless he has already fallen onto the pavement in 5 seconds.

Maximum height of the skyscraper so that the student falls on to the pavement in 5 seconds is:

h= ½gt²=½(10)(25)=125m