NEET Physics: laws of friction Practice Questions

Correct answer: A — greater than kinetic friction

The maximum static friction (f₍s,max)) is the threshold force needed to start motion. The actual static friction force is less than or equal to this maximum value, and kinetic friction is generally greater than static friction (when motion is occurring).

Correct answer: B — The object is at rest or in equilibrium

Static friction acts when there is an attempt to move an object, but it remains at rest. This condition defines the state where the force of static friction balances the applied force, preventing motion.

Correct answer: D — Opposite to the direction of motion

Friction always opposes the relative motion or the tendency of motion between the interacting surfaces.

Correct answer: B — Zero.

According to Newton's First Law, if the velocity is constant (zero acceleration), the net external force acting on the object must be zero. This means the applied forces (like push and friction) must balance each other.

Correct answer: A — Steel and Steel

Generally, the coefficient of friction (μ) is higher for rougher or less smooth surfaces in contact. Therefore, between two rough materials like steel and steel (assuming appropriate conditions), the frictional force tends to be higher than between materials like rubber and rubber, which are often designed for better grip.

Correct answer: C — Kinetic friction

Kinetic friction (or sliding friction) is the friction experienced when two surfaces are in relative motion. It always opposes the direction of motion between them.

Correct answer: C — Limiting friction

The maximum static friction force is called limiting friction. This is the maximum force that friction can exert before the object starts moving.

Correct answer: C — Equal to the force applied

According to Newton's Second Law (F=ma), if friction is zero, the net external force is entirely responsible for the acceleration, following a = F/m.

Correct answer: C — The normal reaction force acting on the object

When an object is at rest, the static friction force balances any unbalanced horizontal forces acting on the object (like applied pushes or pulls). In the absence of other horizontal forces, the static friction force balances the net external horizontal force.

Correct answer: B — Be doubled

The force of friction is directly proportional to the normal force (f ∝ N). If the normal force is doubled, the frictional force will also double.

Correct answer: C — Rolling friction

In rolling motion, the friction responsible for maintaining the rolling action is known as rolling friction.

Correct answer: B — Opposite to the direction of motion

Friction always opposes the relative motion or the tendency of motion between the surfaces in contact.

Correct answer: C — Static friction opposes the initiation of motion while kinetic friction opposes motion once motion is occurring.

Static friction resists the start of motion, and kinetic friction opposes motion once the object is already in motion.