Question

a ball trown vertically upward with a speed of 19.6 m per sec from a top of a tower and returns to the earth in 6sec find the height of the tower

Answer 1

we know that v = u - gt
by squaring on both side, we get

v² = (u²) - 2ugt + (gt)²2
v²2 = (u²2) - 2g (ut -(gt²2)/2)

substitute h in the place of (ut - (gt²2)/2)/
v²2 = (u²2) - 2gh

Here
final velocity is zero.

0 = (u²2) -2gh
2gh = u²2
h = (u²2)/(2g)

where g = 9.8 m²2/s

h = (u²2)/19.6 m
 h = (u²2)/19.6 meter

h = 19.6 m

from

v = u + at

0 = 19.6 - 9.8 * t

t = 2 second to reach from the tower to max height

Now, from maximum height to reach to earth , the time left is 4 seconds

 now, v = 0

S = ut + 1/2 at2

(h+ 19.6) = 0 + 1/2 * 9.8 * 4 * 4

h + 19.6 = 78.4

h = 78.4 - 19.6

h= 58.8 m

MANISHNAVIK1
29/06/2017