a ball is thrown vertically upwards. it rises to a height of h metre in 2.5 seconds,find the initial speed (given, A= 10ms^-2 in the downward direction) 

Initial velocity = 0
Time = 2.5 sec
Displacement = change of position (initial or final)
Given Initial velocity of ball,?u=49?m/s

Let the maximum height reached and time taken to reach that height be?H?and?t?respectively.

Assumption:?g=9.8?m/s2?holds true (maximum height reached is small compared to the radius of earth)


Velocity of the ball at maximum height is zero,?v=0


v2?u2=2aH?? ? ? ? ? ? ? ? ? ? ? ? ?

0?(49)2=2?(?9.8)?H?? ? ? ??

?H=122.5?m?? ? ? ? ? ? ??


v=u+at

0=49?9.8t?? ? ? ? ? ?

?t=5?s

??Total time taken by ball to return to the surface,?T=2t=10?s?