Dynamics Chapter 3 Class 9 Physics KPK Board MCQs | Class Nine Physics Chapter 3 MCQs KPK Board

The downward momentum of gases and the upward momentum of the rocket balance each other, keeping total momentum conserved.

Centripetal acceleration always points toward the center of the circular path.

Atwood’s machine is used to study motion under gravity with two masses and a pulley.

Newton’s First Law is the law of inertia, explaining how objects behave when no force acts on them.

Any force (tension, gravity, friction, or normal force) towards the center produces centripetal acceleration.

A car has large mass and high velocity, giving it high momentum.

Friction in machines wastes energy and causes wear and tear of parts.

Smooth and lubricated wheels reduce resistance, making rolling easier.

Newton’s Second Law states that force produces acceleration in an object.

An isolated system is one where no external force influences the objects inside it.

Without an external unbalanced force, the object cannot start moving.

Force is simply a push or pull that can change the motion or shape of an object.

Friction causes energy loss as heat and wears surfaces over time.

The satellite moves in a circular path, and gravity provides centripetal acceleration toward the Earth.

μ depends on the nature of surfaces, not on the contact area.

The satellite’s motion in a circular orbit is maintained by gravity acting as centripetal force.

Larger μ means surfaces resist motion more, i.e., they are rougher.

Friction between the match and the striking surface produces heat, which lights the match.

Rolling friction is smaller than sliding friction, which is why wheels make motion easier.

The standard unit of force is called Newton (N), named after Sir Isaac Newton.

Pulling hands backward increases the time of momentum change, which reduces the force on hands.

Forces acting between molecules of a substance are called intermolecular forces.

Centripetal force acts towards the center of the circle, keeping the object in circular motion.

Since μ = Friction / Normal force, both in Newtons, units cancel out.

Centripetal acceleration depends on speed (v) and radius (r) of the circular path.

Impulse measures the effect of a force applied over a time, and it changes momentum.

Momentum is conserved only in an isolated system, where external force is zero.

Force can change motion or shape, but it cannot change the mass of an object.

Centripetal force keeps an object moving in a circle by acting toward the center.

A short time interval during which momentum changes results in a very high force.

A satellite moves in a circular path with nearly constant speed, demonstrating uniform circular motion.

Elastic collisions conserve both momentum and kinetic energy.

Linear momentum (p) is calculated using the formula p = m × v.

μ = Frictional force ÷ Normal force, it measures how rough or smooth a surface is.

Weight is directly proportional to g. Lower g → lower weight.

The attractive and repulsive forces between molecules determine the mechanical properties of materials.

Centripetal force depends on mass (m), speed (v), and radius (r) of the circular path.

Even during explosions, the total momentum of an isolated system is conserved.

Since weight is a force, it is measured in Newtons (N).

Repulsive forces prevent molecules from overlapping or coming too close.

Firecrackers release energy suddenly, producing a rapid change in momentum and a strong explosive force.

Rolling friction resists the motion of a body rolling on a surface.

Force is measured in Newtons (N), named after Isaac Newton.

Repulsive forces between molecules in a solid resist compression.

a = v² / r, so if v doubles, a = (2v)² / r = 4(v² / r).

Weight changes because gravity varies at different places, while mass remains constant.

Friction between our shoes and the ground prevents slipping, allowing safe walking.

Gravity pulls the satellite toward the Earth, acting as the centripetal force.

Smooth or polished surfaces reduce resistance to motion and energy loss.

Attractive forces pull molecules toward each other, holding the substance together.

Change in momentum is measured in Newton-seconds (N·s), which is equivalent to kg m/s.

A greater rate of change in momentum means a larger force.

Momentum is conserved only when no external force acts, which is the condition of an isolated system.

Weight depends on mass (m) and gravitational acceleration (g).

The friction between the tires and the road provides centripetal force, allowing the car to turn.

Friction always resists motion between two surfaces in contact.

Both gravity and the normal force act toward the center of the loop, providing centripetal force.

Motion changes only when a force acts on the object (push or pull).

Centripetal acceleration depends on the speed (v) and radius (r) of the circular path.

The slope of the road directs a component of the normal force toward the center, helping in circular motion.

Since momentum = mass (kg) × velocity (m/s), its unit becomes kg m/s.

Momentum is directly proportional to velocity, so more speed → more momentum.

Static friction prevents a stationary object from moving.

Force causes an object to accelerate, which is the main idea of Newton’s Second Law.

Action and reaction forces never act on the same object; they act on two different bodies.

Friction is a force, so its unit is Newton (N).

Increasing the time of impact decreases the force, as seen when using cushions or airbags.

Your forward jump is the action, and the boat’s backward motion is the reaction.

The car keeps moving because of inertia, and stops only when an external force (brakes/friction) acts.

The car loses momentum as it stops; the change in momentum is responsible for the impact force on the wall.

A system is isolated only when the total external force acting on it is zero.

Any force directed toward the center (tension, gravity, friction, etc.) can provide centripetal force.

Newton’s Third Law explains that forces always occur in pairs — action and reaction.

Centripetal acceleration points toward the center, keeping the object in circular motion.

Force is the product of mass (m) and acceleration (a).

When m1 = m2, the forces balance, so the system does not move.

Force equals the rate of change of momentum over time.

Force can be defined as the rate of change of momentum.

Lubricants smoothen surfaces and reduce friction, making motion easier.

Wheels of a car experience rolling friction, which is smaller than sliding friction and helps smooth motion.

F = m × v² / r, so if v doubles, F = m × (2v)² / r = 4 × (m × v² / r).

You apply a force on the wall (action), and the wall applies an equal and opposite force back on you (reaction).

Acceleration a = (m1 − m2)g / (m1 + m2) depends on the difference and sum of the two masses.

By measuring acceleration and masses, Atwood’s machine helps to calculate g experimentally.

In the absence of external forces, total momentum is conserved.

Momentum has both magnitude and direction, so it is a vector.

According to Newton’s Second Law, force = rate of change of momentum.

Rolling friction occurs due to slight deformation of the rolling object and surface.

Newton’s First Law is called the Law of Inertia because it explains how objects resist changes in their motion.

In uniform circular motion, speed is constant, but velocity changes continuously due to changing direction.

To simplify calculations, the pulley is considered massless and frictionless.

Explosions cause a rapid change in momentum, producing a large force over a short time.

Force equals the change in momentum divided by the time over which it acts.

Acceleration is inversely proportional to mass. More mass → less acceleration.

Since momentum = m × v, changing mass or velocity changes momentum.

Conservation of momentum depends on action–reaction forces, which come from Newton’s Third Law.

The rocket pushes gases downward (action), and gases push the rocket upward (reaction).

Weight is the gravitational force that Earth pulls an object with.

μ = F / N = 5 ÷ 20 = 0.25.

Rough surfaces have more interlocking bumps, increasing friction.

The tension in the string pulls the stone toward the center, keeping it in circular motion.

During collision in an isolated system, momentum before = momentum after.

Objects with greater mass have more inertia, meaning they resist changes in motion more strongly.

Without an unbalanced force, the object keeps moving with the same speed and direction.

On frictionless ice, external forces are very small, so the system behaves like an isolated system.