It’s true there are sections in the periodic table that define the elements.
Answer:
(a) 30 m/sec
(b) -50 m/sec
Explanation:
We have given initial velocity of ball u = 50 m/sec
Acceleration due to gravity 
(a) Time t = 2 sec
Now according to first equation of v = u-gt
So v=50-10×2=30 m/sec
(b) Time t = 10 sec
Now according to first equation of motion
So final velocity v = u-gt = 50-10×10 =-50 m/sec
-- We already know the rate of revolutions per time ...
it's 1 revolution per 0.065 sec. We just have to
unit-convert that to 'per minute'.
(1 rev / 0.065 sec) x (60 sec / min) = (1 x 60) / (0.065) = <em>923 RPM</em> (rounded)
_______________________________
-- 1 revolution = 2π radians
(2π rad) / (0.065 sec) = (2π / 0.065) = <em>96.66 rad/sec</em> (rounded)