Question

Angle of repose is equal to the angle of limiting friction. When the body is just at the point of motion, the force of friction in this stage is called limiting friction.

• A. Both assertion and reason are true and reason is the correct explanation of assertion.
• B. Both assertion and reason are true but reason is not the correct explanation of assertion
• C. Assertion is true but reason is false.
• D. Both assertion and reason are false

Answer 1

Answer: (B)

Both assertion and reason are true but reason is not the correct explanation of assertion

Answer 2

The maximum value of static friction up to which body does not move is called limiting friction.
Angle of repose is defined as the angle of the inclined plane with horizontal such that a body placed on it is just begins to slide.
In limiting condition,
$F = mg \sin \alpha$ and $R = mg \cos \alpha$
Where $\alpha=$ angle of repose.
So $\frac{ F }{ R }=\tan \alpha$
$\therefore \frac{ F }{ R }=\mu_{ s }=\tan \theta=\tan \alpha\left(\because \tan \theta=\mu_{ s }\right)$
or $\theta=\alpha$

The angle of limiting friction = Angle of repose

Therefore, the assertion is true.

The frictional force acting on the body just before it begins to move is referred to as limiting friction. Although this is accurate, it doesn't seem to be the right rationale for the situation.

As a result, both the claim and the reason are true, but the reason is not the proper justification for the assertion.

Friction is the opposing force that prevents two solid surfaces, liquid layers, and material components from sliding past one another. The nature of the two surfaces in touch and the force acting on these surfaces are the 2 factors that affect friction There are 2 types of friction forces: Internal friction and External friction.

Under External friction, there is dry friction, fluid friction, skin friction, etc.

Dry friction is further divided into static, kinetic, and rolling friction.

According to microscopic observations, surface imperfections increase friction.

The Laws of Static Friction state -The static friction force is independent of the area of contact between two surfaces.

The Law of Kinetic Friction states- Kinetic friction is a constant force that opposes relative motion.

The Limiting Friction Laws state- The force of limiting friction is independent of the area between two bodies in contact.