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The language of kinematics and motion graphsAQA A-Level Maths: Flashcards

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What is displacement?

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What is displacement?
The change in position; a vector with magnitude and direction.
What is distance travelled?
The total length of the path; a scalar.
Average velocity formula?
displacementtime\frac{\text{displacement}}{\text{time}}.
Average speed formula?
total distancetime\frac{\text{total distance}}{\text{time}}.
What is acceleration?
The rate of change of velocity.
Which are vectors: speed, velocity, distance, displacement, acceleration?
Velocity, displacement and acceleration.
Gradient of a displacement-time graph?
The velocity.
Gradient of a velocity-time graph?
The acceleration.
Area under a velocity-time graph?
The displacement.
What does a horizontal line on a displacement-time graph mean?
The object is at rest.
What does a negative gradient on a displacement-time graph mean?
The velocity is negative: moving in the negative direction.
Why can average velocity be zero while average speed is not?
For a round trip the displacement is zero but the distance travelled is not.
Area of a trapezium for a velocity-time graph?
12(a+b)h\frac12(a+b)h where aa and bb are the parallel sides.

Exam questions on The language of kinematics and motion graphs

  1. A runner starts at point OO on a straight track and runs 4040 m in the positive direction in 88 s. She then immediately turns round and runs 1515 m back towards OO in 55 s.
    Find the average speed of the runner over the whole 1313 s, and explain why it is different from the magnitude of her average velocity.2 marks
  2. A train travels along a straight track. Its velocity-time graph is made of three straight-line sections: the velocity increases uniformly from 00 to 2020 m s−1^{-1} in 1010 s, then stays constant at 2020 m s−1^{-1} for 3030 s, then decreases uniformly to 00 in 2020 s.
    Find the acceleration of the train in the last 2020 s, and state what the sign of your answer tells you.2 marks
  3. A cyclist travels along a straight road. Her displacement ss metres from a point OO, at time tt seconds, has a displacement-time graph made of three straight-line sections: ss increases uniformly from 00 to 100100 when tt goes from 00 to 2020; ss stays at 100100 from t=20t=20 to t=50t=50; and ss decreases uniformly from 100100 to 4040 from t=50t=50 to t=80t=80.
    Find the velocity of the cyclist in each of the three stages of her journey.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).