Weight of the stone = 500 N
Area of contact = 25 cm²
Pressure = \(\cfrac { force }{ area } \)
= \(\cfrac { 500 }{ 25 } \)
= 20 Nm^-2 or pascal

a) If both assertion and reason are true and the reason is the correct explanation of the assertion

c. Assertion is true, but reason is false.

a. Both assertion and reason are true and reason is the correct explanation of assertion.

Ball bearings

Static, Rolling

Lack of friction between the feet and the banana peels.

To get a better grip.

i) The pressure exerted by the mercury column in a barometer is considered as the pressure of magnitude 'one atmosphere'.
ii) 1 atm = pressure due to 76 cm of mercury column in a barometer = 1.01 x 10⁵ Nm^-2.

The instruments Manometer, Bourdon gauge help to pressure of a fluid.

i) When a kicking force is exerted on a football at rest, it raises.
ii) When a pushing force is applied on a box at rest it moves.

From Boyle's law :- P α 
Initial Pressure P₁  = atmospheric pressure + pressure of liquid cloumn
= Hρg + Hρg
Where h 2 depth of the pond
H 2 Assume 10m of water
V₁ = \(\frac { 4 }{ 3 } \pi \)r³ ; P₂ = Hρg
V₂ = \(\frac { 4 }{ 3 } \pi \)(3r)³ = \(\frac { 4 }{ 3 } \pi \)(27r³)
P₁V₁ = P₂V₂ 

​​​​​​​h+10 =10x27
h =270-10
depth of the pond, h = 260m

Ways to minimise friction
(i) By applying lubricants like grease and cocount oil.
(ii) By using ball bearing we can change sliding friction to rolling friction
(ii) By smoothening the surface of contact of the moving bodies rather than irregular surfaces.

Frictional force arises when two or more bodies in contact move or tend to move, relative to each other. It acts always in the opposite direction of the moving body.
Examples:
(i) To light a matchstick.
(ii) To stitch a cloth in a sewing machine.

i. The level of mercury is initially at the same level.
ii. The gas present in the manometer event pressure.
iii. The mercury level moves down in one limb and rises in other limb.
iv. The mercury level moves down in one limb and rises in other limb.
v. The difference in liquid pressure is measured.

Friction is a necessary evil:
Though friction is giving a negative effect in most of our day to day life, it helps us to make our life easy. So, it is called as 'necessary evil'.
Advantages of friction:
i) We can hold any object in our hand due to friction.
ii) We can walk on the road because of friction.
iii) The footwear and the ground help us to walk without slipping
iv) Writing easily with a pen on paper is due to friction.
v) Automobiles can move safely due to friction between the tyres and the road.
vi) Brakes can be applied due to frictional resistance on brake shoes.
vii) We are able to light a matchstick, sew clothes, tie a knot or fix a nail in the wall because of friction
Disadvantages of friction :
i) Friction wears out the surfaces rubbing with each other like screws and gears in machines or soles of shoes.
ii) To overcome the friction an excess amount of effort has to be given to operate a machine. This leads to wastage of energy.
iii) Friction produces heat, which causes physical damage to the machines