Cambridge AS and A Level Physics (9702) Syllabus

Distinguish between displacement and distance.

Distance is the total path length travelled (scalar). Displacement is the straight-line distance from start to finish in a specified direction (vector).

Distinguish between speed and velocity.

Speed is the rate of change of distance (scalar). Velocity is the rate of change of displacement (vector), having both magnitude and direction.

On a displacement-time graph, what does the gradient represent?

The gradient (slope) of a displacement-time graph represents the velocity. A curved line indicates changing velocity (acceleration).

On a velocity-time graph, what do the gradient and the area under the line represent?

The gradient represents acceleration; the area under the line represents displacement.

How can you determine instantaneous velocity from a curved displacement-time graph?

Draw a tangent to the curve at that point and find its gradient.

What does a horizontal line represent on a velocity-time graph versus a displacement-time graph?

On a velocity-time graph a horizontal line means constant velocity (zero acceleration). On a displacement-time graph a horizontal line means the object is stationary.

In projectile motion, how do the horizontal and vertical motions relate?

They are independent. Horizontal velocity is constant (no horizontal force, ignoring air resistance); vertical motion has constant downward acceleration g due to gravity.

For a projectile launched at speed u and angle θ, what are the initial horizontal and vertical velocity components?

Horizontal: u cos θ (constant). Vertical: u sin θ (decreasing under gravity).

What is the velocity at the highest point of a projectile's trajectory?

The vertical component is zero; the velocity equals the (constant) horizontal component u cos θ. The acceleration is still g downward.

How does air resistance affect a projectile's trajectory?

It reduces the range and maximum height, makes the path asymmetric (steeper on descent), and reduces both horizontal and vertical velocity components over time.

State Newton's first law of motion.

An object remains at rest or in uniform motion in a straight line unless acted upon by a resultant (net) external force.

State Newton's second law of motion.

The rate of change of momentum of an object is directly proportional to the resultant force acting on it and occurs in the direction of that force: F = Δp/Δt, giving F = ma for constant mass.

State Newton's third law of motion.

When body A exerts a force on body B, body B exerts an equal and opposite force on body A. The forces are of the same type and act on different bodies.

Why must Newton's third law force pairs act on different bodies?

Because action and reaction are forces exerted by two different objects on each other; if both acted on the same body they would cancel and nothing could ever accelerate.

Define linear momentum and give its unit.

Linear momentum p = mass x velocity (p = mv). It is a vector quantity with unit kg m s^-1 (equivalently N s).

State the principle of conservation of linear momentum.

For a system with no external resultant force, the total linear momentum before an interaction equals the total linear momentum after: total p is conserved.

Define impulse and relate it to momentum.

Impulse = force x time (F Δt) and equals the change in momentum: F Δt = Δp = mv - mu. Unit: N s.

Distinguish between elastic and inelastic collisions.

In an elastic collision both momentum and kinetic energy are conserved. In an inelastic collision momentum is conserved but kinetic energy is not (some converts to other forms). Momentum is conserved in both.

What is a perfectly inelastic collision?

A collision in which the colliding objects stick together and move with a common velocity afterwards; momentum is conserved but the maximum possible kinetic energy is lost.

For a 1D elastic collision, what is true of the relative velocity of approach and separation?

The relative speed of approach equals the relative speed of separation: (u1 - u2) = (v2 - v1).

Distinguish between mass and weight.

Mass is the amount of matter in a body (scalar, kg), constant everywhere. Weight is the gravitational force on the mass (vector, N), W = mg, and varies with gravitational field strength.

Define gravitational field strength and give its formula and unit.

Gravitational field strength g is the gravitational force per unit mass: g = F/m = W/m. Unit: N kg^-1 (numerically equal to acceleration of free fall in m s^-2).

What is the approximate value of g near Earth's surface and what does it represent?

g ≈ 9.81 N kg^-1 (or 9.81 m s^-2). It is the gravitational field strength / acceleration of free fall near Earth's surface.

Define the moment of a force.

The moment of a force is the product of the force and the perpendicular distance from the pivot to the line of action of the force: moment = F x d. Unit: N m.

Define a couple and state the torque of a couple.

A couple is a pair of equal, opposite, parallel forces whose lines of action do not coincide. Its torque = one force x perpendicular distance between the forces (F x d).

State the principle of moments.

For a body in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about that same point.

What are the two conditions for a body to be in equilibrium?

1) The resultant force in any direction is zero (forces balance). 2) The resultant moment (torque) about any point is zero (principle of moments).

How can three non-parallel coplanar forces in equilibrium be represented geometrically?

They form a closed triangle of forces when drawn head-to-tail (their vector sum is zero), and their lines of action pass through a single point.

Define density and give its formula and SI unit.

Density is mass per unit volume: ρ = m/V. SI unit: kg m^-3.

Define pressure, give its formula and unit, and state the equation for pressure in a fluid column.

Pressure is force per unit area: p = F/A, unit pascal (Pa = N m^-2). Pressure due to a fluid column of height h: p = ρgh.