What is the force of friction? State two methods to reduce friction.

What is the force of friction? State two methods to reduce friction.

Ans: – The force of friction is the restricted force principal when an object is moving slow its speed.

Method for the reduction of friction: –

• Using lubricating oil.
• By polishing the surface.

 

An object of mass 2 kg travelling in a straight line with a velocity of 10ms–1 collides with and sticks to a stationary object of mass 6 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact.

Ans: – Momentum= mass × velocity;

Here, mass= (2 + 6) = 8kg. And velocity= 10m/s.

So, momentum= 8×10= 80. Khm/s^2.

 

What is the relation between thrust and pressure? State the SI units of thrust and pressure. Why a camel can run in a desert easily?

Ans: – Thrust and pressure are directly proportional to each other.

The SI unit of thrust is Newton and the pressure is Pascal.

Because of having wide feet and the long leg the camel loses its weight in the sand and as a result of that easily runs on the surface of the desert.

 

A block of wood kept on a table applies a thrust of 49 N on the table top. The dimensions of the wooden block are 40 cm × 20 cm × 10 cm. Calculate the pressure exerted by the wooden block if it is made to lie on the table top with its sides of dimensions (a) 20 cm × 10 cm and (b) 40 cm × 20 cm.

Ans: – We know that, pressure = force/ area,

Case: – 1;

Here area = 20×10 cm^2 = 0.2× 0.1 m^2.

So, pressure= 49 / (0.2 × 0.1) =2450pa.

Case: – 2;

Here, area= 40× 20 cm^2 = 0.4 × 0.2 m^2.

So, pressure= 49 / (0.4 × 0.2) =612.5 pa.

 

 

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