Answer:
a) 
b) 
Explanation:
Given:
- mass of the ball thrown up,
- initial velocity of the ball thrown up,
- height above the ground from where the ball is thrown up,
a)
Maximum height attained by the ball above the roof level can be given by the equation of motion.
As,
where:
final velocity at the top height of the upward motion 
acceleration due to gravity
height of the ball above the roof
Now,
Therefore total height above the ground:
b)
Now we find the time taken in raching the height 
:
final velocity at the top of the motion
So,
Now the time taken in coming down to the ground from the top height:
where:
is the initial velocity of the ball in course of coming down to ground from the top
Here the direction acceleration due to gravity is same as that of motion so we are taking them positively.
Therefore the total time taken in by the ball to hit the ground after it begins its motion:
<span>When the electric current flows out of the
page and the direction of the magnetic field is counter-clockwise. The magnetic
field that is made by an electric current is said to be always leaning
perpendicularly to the direction of the current flow.</span>
Air is a mixture.
as per definition, mixture is a combination we get after adding two or more things together in any proportion.
air is a mixture because it contains a number of gases like nitrogen , oxygen, carbon dioxide. it also contains dust particles, small organisms, water vapors etc.
carbon monoxide is not a mixture as it is formed from fixed proportion of carbon and oxygen.
similarly, water is is not a mixture as it is formed from fixed proportion of hydrogen and oxygen.
Power is the rate of doing work.
Its unit is joules/second.
That unit is used so often that a new word was adopted for it.
1 joule/sec = 1 watt
