Dynamics of Linear Motion – Topic 3 Review

These question-and-answer flashcards cover key definitions, formulas, laws, and concepts from Topic 3 – Dynamics of Linear Motion, including momentum, impulse, conservation principles, common forces, free-body diagrams, friction, and Newton’s three laws of motion.

What is linear momentum and its SI unit?

Momentum p is the product of an object’s mass and velocity (p = m v); it is a vector with SI unit kg·m s⁻¹ (or N·s).

How can you resolve a momentum vector into components?

Use pₓ = p cos θ and pᵧ = p sin θ, then p = √(pₓ² + pᵧ²) and θ = tan⁻¹(pᵧ/pₓ).

Define impulse and give its formula.

Impulse J is the product of force and the time interval of action: J = F Δt = Δp = m(v – u).

What is the SI unit of impulse?

Impulse is measured in N·s, the same as kg·m s⁻¹.

What does the shaded area under an F–t graph represent?

The impulse delivered to the object, J = area under the force–time curve.

State the Principle of Conservation of Linear Momentum.

For an isolated system (ΣFext = 0), total momentum before interaction equals total momentum after: Σpi = Σp_f.

Write the 1-D conservation of momentum equation for two masses.

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂.

What two conditions define an elastic collision?

(1) Total momentum is conserved, (2) total kinetic energy is conserved.

What distinguishes an inelastic collision from an elastic one?

Momentum is still conserved, but total kinetic energy is not; some converts to other forms (heat, sound, deformation).

Do inelastic collisions always result in objects sticking together?

No. Sticking (perfectly inelastic) is one case; many inelastic collisions separate after impact.

Give the equation for static friction.

fs ≤ μs N, with maximum fs(max) = μs N.

Give the equation for kinetic (dynamic) friction.

fk = μk N, where μk < μs for the same surfaces.

List the five common forces identified in a free-body diagram for this course.

Weight (W), Tension (T), Normal force (N), Friction (f), External push/pull force (F).

Define weight and provide its direction and formula.

Weight W is the gravitational force on a mass: W = m g, always directed vertically downward toward Earth’s centre.

Define tension in a light, inextensible string.

Tension is the pulling force along the string, directed away from the object; it is the same everywhere in a massless, frictionless cord.

Define the normal force.

A contact force exerted by a surface on an object, acting perpendicular to the surface.

Define frictional force.

A force parallel to the surface that opposes relative motion or the tendency of motion between two contacting surfaces.

What is the definition of one newton (1 N)?

The net force that gives a 1 kg mass an acceleration of 1 m s⁻².

State Newton’s First Law of Motion.

An object remains at rest or moves with constant velocity in a straight line unless acted upon by a net external force.

What is inertia and on what does it depend?

Inertia is a body’s tendency to resist changes in motion; it depends solely on the object’s mass.

When is a particle in equilibrium?

When the vector sum of all forces is zero (ΣF = 0); acceleration is zero.

State Newton’s Second Law in its simplest form.

The net force on an object equals mass times acceleration: ΣF = m a.

How do you set up ΣF = m a in a chosen direction?

(Forces in direction of a) minus (forces opposite to a) equals m a.

State Newton’s Third Law of Motion.

For every action force there is an equal-magnitude, opposite-direction reaction force acting on a different body (FAB = –FBA).

Why don’t action-reaction forces cancel?

They act on different bodies; only forces on the same body can cancel in ΣF.

Give the apparent weight in an elevator accelerating upward with acceleration a.

Normal force N = m(g + a).

Give the apparent weight in an elevator accelerating downward with acceleration a.

Normal force N = m(g – a).

On an inclined plane, what are the components of weight?

Parallel to plane: W∥ = m g sin θ; Perpendicular: W⊥ = m g cos θ.

What is an impulsive force?

A large force acting for a very short time interval during a collision or impact, producing an impulse.

Express the impulse–momentum theorem.

J = Δp; the impulse acting on a body equals its change in momentum.

Momentum and force are examples of what type of physical quantity?

Vector quantities (they have both magnitude and direction).

What does friction NOT depend on, according to the notes?

The area of contact between the two surfaces.

Compare the relative sizes of μs and μk.

The coefficient of static friction is greater than that of kinetic friction (μs > μk).

Write the normal reaction force for a block at rest on an incline.

N = m g cos θ.

In a perfectly elastic collision, what happens to total kinetic energy?

It is conserved; Kinitial = Kfinal.

Give an everyday example showing that high momentum can come from large mass or high velocity.

A charging elephant (large mass) and a speeding bullet (high velocity) both have large momentum and are hard to stop.

What is the formula for system acceleration when blocks are pulled by a force F on a frictionless surface?

a = F / Σm (sum of the masses in the system).

What is the net external force condition for applying conservation of momentum?

ΣF_ext = 0; the system must be isolated or external forces must cancel.

What does the shaded area under a variable force–time curve equal?

The impulse delivered: J = ∫ F dt (area under the curve).

Why can momentum be conserved while kinetic energy is lost?

Because momentum is a vector conserved in all collisions in an isolated system, whereas kinetic energy can transform into other energy forms (heat, sound, deformation).