NEET Physics: Friction questions with solutions

Q1. Can friction ever be eliminated?

1. Yes
2. No
3. Sometimes
4. Depends on the object in regard

Answer: No

Friction arises from microscopic interactions between surfaces, so it cannot be completely removed in real-world conditions. It can be minimized with lubrication or special materials, but not eliminated entirely.

Q2. The force of friction is normal reaction between the surfaces.

1. Inversely propotional to
2. directly propotional to
3. propotional to the square of
4. independent of

Answer: directly propotional to

For dry friction, the frictional force is modeled as F = μN, where N is the normal reaction. Since μ is constant for a given pair of surfaces, friction increases directly with the normal reaction.

Q3. The static frictional force is

1. self adjustable.
2. not self adjustable.
3. scalar quantity.
4. equal to the limiting force.

Answer: self adjustable.

Static friction is called self-adjustable because it varies in magnitude to oppose the applied force as needed, until it reaches its maximum value. It is not always equal to the limiting friction; that only happens at the threshold of motion.

Q4. A block B of mass \( 4 \mathrm{kg} \) is placed on a rough horizontal plane. A time dependent horizontal plane. A time dependent horizontal force \( \boldsymbol{f}=\boldsymbol{k} \boldsymbol{t}^{2} \) acts on the block, \( k=2 N / s^{2} . \) The frictional force between the block and the plane at \( \boldsymbol{t}=2 \sec \) is \( \boldsymbol{\mu}=\mathbf{0 . 2} \)

1. 4 N
2. 8N
3. 12 N
4. zero

Answer: 8N

At t = 2 s, the applied force is f = kt^2 = 2×(2^2) = 8 N. Since the block is on a rough horizontal plane, the frictional force at that instant matches the opposing force up to its limiting value, which here is consistent with 8 N.