Cambridge O Level Physics 5054 Syllabus

For an object falling from rest, how do its speed and the distance fallen change each second (ignoring air resistance)?

Speed increases uniformly by g each second (constant acceleration); the distance fallen each successive second increases.

What is terminal velocity?

The constant maximum velocity reached by a falling object when air resistance (drag) equals its weight, so the resultant force and acceleration are zero.

State Newton's First Law of motion.

An object remains at rest, or continues moving at constant velocity, unless acted on by a resultant (unbalanced) force.

State Newton's Second Law as an equation and define the terms.

F = m a, where F is the resultant force (N), m is mass (kg) and a is acceleration (m/s^2).

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 (action and reaction are equal and opposite).

Define the newton (N).

One newton is the force that gives a mass of 1 kg an acceleration of 1 m/s^2 (1 N = 1 kg m/s^2).

What is the difference between mass and weight?

Mass is the amount of matter in a body (kg) and is constant. Weight is the gravitational force on it (N) and varies with g; W = m g.

Define gravitational field strength (g) and give its unit.

Gravitational field strength is the force per unit mass on an object, g = W/m. Unit: N/kg (numerically equal to the acceleration of free fall).

What is friction and in which direction does it act?

Friction is a contact force that opposes (acts against) the relative motion or tendency of motion between two surfaces.

Give two effects of friction, one useful and one undesirable.

Useful: allows grip/walking and braking. Undesirable: causes wear and produces heat, wasting energy.

What is a resultant force?

The single force that has the same effect as all the forces acting on an object combined (their vector sum).

What happens to an object when the resultant force on it is zero?

It stays at rest or continues to move with constant velocity (forces are balanced; equilibrium).

Define the moment of a force and give its formula and unit.

The moment is the turning effect of a force about a pivot: moment = force x perpendicular distance from the pivot (F x d). Unit: newton metre (N m).

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 point.

State the two conditions for a body to be in equilibrium.

1) The resultant force is zero (forces balance). 2) The resultant moment about any point is zero (clockwise moments = anticlockwise moments).

What is the centre of gravity of an object?

The single point through which the whole weight of the object appears to act.

How does the position of the centre of gravity affect stability?

A lower centre of gravity and a wider base give greater stability (the object is less likely to topple).

State Hooke's Law.

The extension of a spring is directly proportional to the force (load) applied, provided the limit of proportionality is not exceeded.

Write the equation linking force and extension for a spring.

F = k x, where F is force (N), k is the spring constant (N/m) and x is the extension (m).

What is the limit of proportionality (elastic limit) on a load-extension graph?

The point beyond which extension is no longer proportional to load; beyond the elastic limit the material no longer returns to its original length (permanent deformation).

On a load-extension graph for a spring, what does the gradient of the linear region represent?

It relates to the spring constant k (a steeper line means a stiffer spring with a larger k).

State the principle of conservation of energy.

Energy cannot be created or destroyed; it can only be transferred from one form (store) to another, and the total energy remains constant.

List five different forms (stores) of energy.

Kinetic, gravitational potential, chemical, elastic (strain), thermal (internal), nuclear, electrical, light and sound.

Write the formula for kinetic energy.

KE = (1/2) m v^2, where m is mass (kg) and v is speed (m/s). Unit: joule (J).

Write the formula for gravitational potential energy.

GPE = m g h, where m is mass (kg), g is gravitational field strength (N/kg) and h is height (m).

Define work done and give its formula and unit.

Work done is energy transferred when a force moves its point of application: W = F x d (force x distance moved in the direction of the force). Unit: joule (J).

Define power and give its formula and unit.

Power is the rate of doing work or transferring energy: P = W/t (or E/t). Unit: watt (W), where 1 W = 1 J/s.

Define efficiency and give the formula.

Efficiency is the fraction of input energy usefully transferred: efficiency = (useful energy or power output / total energy or power input) x 100%.

Why is no real machine 100% efficient?

Because some energy is always transferred (dissipated) to the surroundings in less useful forms, usually as heat due to friction (and sometimes sound).

Name four renewable energy resources.

Solar, wind, hydroelectric, tidal, wave, geothermal and biofuel (any four).

What is the original source of most of the energy we use, and which two resources do NOT derive from the Sun?

Most energy originates from the Sun (e.g. fossil fuels, wind, hydro, biofuels). Geothermal and nuclear (and tidal, which is mainly from the Moon) do not come from the Sun.