Question

a boy throws a ball upwards, and after 8 seconds, he catches it again. then find:
(a) By which velocity was the ball thrown upward?
(b) At what height, the velocity of the ball will be zero?

Answer 1

Let the initial velocity (velocity by which ball was thrown be u).

Then final velocity v = 0.

Acceleration a = 9.8 m/s2.

From 1 eq of motion :

V = u + at

0 = u + - 9.8 ☓ 8.

U = 78.4 m/s

I I) let the height to which ball rises be h. Then,

V = 0, u = 78.4, a = 9.8 m/s2

From 3 eq of motion :

V^2 = u^2 + 2ah

0 = 78.4 ☓ 78.4 + 2 ☓- 9.8 ☓ h.

0 = 6146.56 - 19.6 h

19.6 h = 6146. 56 m

h = 313.6 m

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Note : a = acc due to gravity = 9.8 m/s2

If u take it as 10 then ans may vary.

The v = 0 at the highest point to which the ball rises