Question 1

What is the difference between speed and velocity?

Accepted Answer

Speed is a scalar quantity that measures how fast an object is moving, regardless of direction. Velocity is a vector quantity that includes both speed and direction. For example, a car travelling at 30 m/s north has a velocity of 30 m/s north, but its speed is just 30 m/s. If the car turns, its velocity changes even if its speed stays the same.

Question 2

How do you calculate acceleration from a velocity-time graph?

Accepted Answer

Acceleration is given by the gradient (slope) of a velocity-time graph. To calculate it, choose two points on the line, find the change in velocity (Δv) and the change in time (Δt), then use the formula: acceleration = Δv / Δt. For a straight line, this is constant acceleration. If the line is curved, the acceleration is changing, and you would need to draw a tangent to find the instantaneous acceleration.

Question 3

What is Newton's second law and how do I use it?

Accepted Answer

Newton's second law states that the resultant force acting on an object is equal to the rate of change of its momentum, or more simply, F = ma, where F is the resultant force in newtons, m is the mass in kilograms, and a is the acceleration in m/s². To use it, identify all forces acting on the object, find the resultant (net) force, then rearrange to find acceleration or mass. For example, if a 5 kg object experiences a resultant force of 20 N, its acceleration is 20/5 = 4 m/s².

Question 4

How do I calculate stopping distance and what factors affect it?

Accepted Answer

Stopping distance = thinking distance + braking distance. Thinking distance is the distance travelled during the driver's reaction time (typically 0.2–0.9 s), calculated as speed × reaction time. Braking distance depends on speed, mass, and braking force. Factors that increase stopping distance include higher speed, poor road conditions (wet/icy), worn tyres, and driver impairment (alcohol, fatigue). The faster you go, the greater the stopping distance—doubling speed roughly quadruples braking distance.

Question 5

What is the conservation of momentum and how is it applied in collisions?

Accepted Answer

The principle of conservation of momentum states that in a closed system (no external forces), the total momentum before an event equals the total momentum after the event. For collisions, you can use: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂. For example, if a 2 kg ball moving at 3 m/s hits a stationary 1 kg ball, and they stick together, the combined mass is 3 kg. Total momentum before = 2×3 + 1×0 = 6 kg m/s. After, velocity = 6/3 = 2 m/s. This principle is also used in explosions (e.g., rockets).

Question 6

How do I draw and interpret distance-time graphs?

Accepted Answer

On a distance-time graph, distance is on the y-axis and time on the x-axis. A straight horizontal line means the object is stationary (zero speed). A straight sloping line means constant speed—the steeper the slope, the faster the speed. A curved line indicates changing speed (acceleration or deceleration). To find speed from a straight line, calculate the gradient: change in distance / change in time. For a curved line, draw a tangent at the point of interest to find instantaneous speed.

Topic 2 – Motion and forces

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Likely Command Words

Ready to test yourself?

Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

How to Revise Topic 2 – Motion and forces — Edexcel GCSE Physics

Examiner Tips for Topic 2 – Motion and forces

Common Mistakes in Topic 2 – Motion and forces

Key Marking Points