Q38. Help me Please A man throws balls with the same speed vertically
upwards one after the other at an interval of
2 second. What should be the speed of the throw
so that more than two balls are in the sky at any
time? (Given g = 9.8 m/s2)
(1) More than 19.6 m/s
(2) At least 9.8 m/s
(3) Any speed less than 19.6 m/s
(4) Only with speed 19.6 m/s

The correct option is A.

We have t=2s

When the ball is thrown upward the final velocity become zero.

Therefore,

v=u+at

0=u−gt  

Here, g is acceleration due to gravity

u=gt

=9.8×2=19.6 m/s

Thus, when he throws a ball with a minimum speed of 19.6m/s in a time interval of 2s.

Then two balls can be in the air simultaneously.

in simple terms, the principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g. this is also known as upthrust.