IGCSE Physics · 0625

IGCSE Physics: Motion, Speed and Acceleration Questions

Motion questions test both calculation and graph reading. These worked examples cover acceleration from a change in velocity, reading distance from a velocity-time graph and interpreting the gradient of a distance-time graph.

What you need to know

Speed equals distance divided by time; acceleration equals change in velocity divided by time taken.
On a distance-time graph, the gradient is the speed.
On a velocity-time graph, the gradient is the acceleration and the area under the line is the distance travelled.
Acceleration is measured in metres per second squared (m/s squared).

On a velocity-time graph, a sloping line shows acceleration and a flat line shows constant velocity.

Practice questions with answers

Question 12 marks

A car accelerates from rest to 20 m/s in 8 seconds. Calculate its acceleration.

Acceleration = change in velocity divided by time = (20 minus 0) divided by 8 = 2.5 m/s squared.

Mark schemeCorrect method, change in velocity over time (1). Correct answer 2.5 m/s squared with unit (1).

Common mistakeForgetting the unit, or dividing time by velocity.

Exam tipFrom rest means the starting velocity is zero. Do not forget the unit m/s squared.

Question 23 marks

On a velocity-time graph, a car travels at a constant 15 m/s for 10 seconds. Calculate the distance travelled.

The distance is the area under the velocity-time graph. For constant velocity this is a rectangle: distance = velocity times time = 15 times 10 = 150 m.

Mark schemeRecognise distance is the area under the graph (1). Area = velocity times time (1). Answer 150 m (1).

Common mistakeReading the gradient instead of the area when asked for distance.

Exam tipOn a velocity-time graph: gradient gives acceleration, area gives distance. Decide which the question wants.

Question 32 marks

State what the gradient of a distance-time graph represents.

The gradient of a distance-time graph represents the speed of the object. A steeper gradient means a greater speed.

Mark schemeGradient represents speed (1). Steeper means faster, or a flat line means stationary (1).

Common mistakeConfusing distance-time with velocity-time graphs.

Exam tipOn a distance-time graph a horizontal line means the object is stationary, not moving at constant speed.

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Frequently asked questions

What is the formula for acceleration?

Acceleration equals the change in velocity divided by the time taken. It is measured in metres per second squared.

How do you find distance from a velocity-time graph?

Calculate the area under the line. For a rectangle it is velocity times time; for a triangle it is half base times height.

What is the difference between speed and velocity?

Speed is how fast an object moves. Velocity is speed in a stated direction, so it is a vector quantity.

What does a flat line on a distance-time graph mean?

A horizontal line means the distance is not changing, so the object is stationary.

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