1.What do you mean by pressure?

Pressure is the thrust applied per unit area. It is expressed as the ratio of force to that of area on which it is applied.
                                      
                       Unit of pressure is N/m² or 'Pascal'.    

2.Write down the relation between Pressure P Force F and Area A.

We know that,
                     
From this we can say that pressure is directly proportional to the force applied on a surface greater the force applied on a surface, grater is the pressure.
Also, pressure is inversely proportional to surface area. For smaller contact area pressure would be large and vice versa.

3.Take a carry bag and fill it with 5kg of rice. Now take a thin rope and make a handle of it for the bag and hang the bag on your shoulder with it. Then take a sheet of cloth 4 inches broad and make handle with it and hang the bag on your shoulder. In which of the above cases you feel more pressure on your shoulder and why?

In the first case we felt more pressure. This is because in  the  first case the area of the surface in contact with our shoulder is very small. Since pressure is inversely proportional to surface area we felt more  pressure. In the second case the area of the contacting surface is not so small and we felt less pressure on our shoulder.

4. Straps of school bags are made broad. Why?

Straps of school bags are made broad because when we use broad straps the weight of the bag is spread over the layer area on the shoulder and pressure experienced is less.

5.Tyres of vehicles are deflated in deserts. Why?

Tyres of vehicles are deflated in deserts in order to increase the contact area with the ground. As the contact area increases the exerting pressure will be less and the jeep does not sink.

6.It is difficult to walk on fresh snow but you can ski on it. Why?

It is difficult to walk on fresh snow because we will crash the surface with our weight. But when we ski on it there arise no difficulties as skis have large surface area and cause less pressure on the snow.

7.What are fluids? do they also exert pressure?

Liquids, gases and plasmas which flow under stress are together called fluids./ Fluids also exert pressure. The pressure exerted by atmosphere is called atmospheric pressure.

8.We can not feel the atmospheric pressure. Why?

We cannot feel the atmospheric pressure because it is balanced by the internal pressure of the body exerted by the body fluids.

9.What is the pressure exerted on the floor by a boy of weight 75 N, if the contact surface area of the feet is 0.075 m² ?

We have,
            

10.What will be the area of a surface where a force of 2500N produces a pressure of 25 Pa on it?

We have,
            

11.Suppose a force of 5000N produces a pressure of 10,000 Pa, then calculate the new pressure if the force is increased by 3 times?

We have,
           

If force increase by 3 times, pressure also become 3 times.

12.Why camels are used in deserts for transportation?

The surface area of camels foot is large and hence the pressure exerted on the ground will be less and it will not sink. So we use camels in deserts for transportation.

13.What effect will it have on the force required if the pressure increase 10 times the original value and area becomes half of the original value?

We have,
        
Force become 5 times of its original value.

14.Derive the unit of pressure in terms of force and area?

We know that
                Pressure 
The SI unit of force F is N and that  of area is m²
Then Unit of  

Unit of pressure is Nm-2. It is also called 'Pascal'.

15.Find the area of the school bag strap n contact with your shoulders if the weight of the bag is 100N and pressure exerted by the bag on your shoulders is 20,000 Pa?