Question

21.
A body thrown vertically up from ground passes the
height of 25 m twice in an interval of 4 sec. The
initial velocity of body is -
(A) 30 ms-1
(B) 20 ms!
(C) 50 ms 1
(D) 40 ms-1​

Answer 1

Answer:

(A) - 30 m/s

Explanation:

Lets assume the initial velocity to be u.

s = 25, u =u, a = -g

v² - u² = 2as

v² = u² - 50g -------- (1)

After 25 m is crossed, the time of flight to return back to the same point is

T = 2v/g

4 = 2v/10 ,  v = 20

Substitute v in equation 1

20² = u² - 50(10)  

900 = u²

u = 30