Aball is thrown vertically upwards with an initial velocity of 20.00 m/s. neglecting air resistance, how long is the ball in the air? what is the greatest height reached by the ball? also calculate the time at which the ascending ball reaches a height of 15 m above the ground.

1) The greatest height attained by the ball equals 20.387 meters.

2) The time it takes for the ball to reach 15 meters approximately equals 1 second.

Explanation:

The greatest height will be attained when the ball stop's in the air and starts falling back to the earth.

thus using third equation of kinematics we obtain the height attained as

where

'v' is the final speed of the ball

'u' is the initial speed of the ball

'a' is the acceleration that the ball is under which in this case equals 9.81

's' is the distance it covers

Thus for maximum height applying the values in the equation we get

Using the same equation we can find the speed of the ball when it reaches 15 meters of height as  

the time it takes to reduce the velocity to this value can be found by first equation of kinematics as

learn it on the intertant so you can solve

force is mass*acceleration.

we have a very small mass: 11.4*0.001 kg

if we want 0.035n of force, we need an acceleration:

0.035 = 11.4*0.001*a

a = 0.035/(11.4*0.001) m/s^2