Part-I: When the ball will reach the highest point then the final velocity will be zero. Initial velocity = u m/sec, final velocity = 0 m/sec, acceleration = -g m/sec‌2 applying 1st equation of motion v = u + at 0=u−gt1 t1=
u
g
Part-II: Initial velocity will be zero as the ball is at the highest point. applying 1st equation of motion v = u + at 3u=0+gt2 t2=