Friction

Question 1:

A horizontal force of 10 N is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is 0.2. The weight of the block is

1. 20 N

2. 50 N

3. 100 N

4. 2 N

View Answer

Maximum Friction force action on an object is μN.

Here μ=0.2 and Normal reaction force will be equal to applied force i.e 10 N.,

So, friction force is 0.2*10 = 2N

Question 2:

An insect crawls up a hemispherical surface very slowly (see the figure). The coefficient of friction between the insect and the surface is 1/3. If the line joining the centre of the hemispherical surface to the insect makes an angle a with the vertical, the maximum possible value of α is given by :

1. cot α = 3

2. tan α = 3

3. sec α = 3

4. cosec α = 3

View Answer

For Equilibrium,

⇒ μmg cos θ = mg sin θ

⇒ μ = tan θ = 1/3

⇒ cot θ = 3