Forces and Motion
6 marks · NormalA cyclist travels along a straight road and then up a hill. The cyclist's motion is monitored using different methods. Use the data and diagrams to answer the questions.
State the SI units for mass, distance, average speed, and force.
The cyclist covers 1500 m in 300 s. Calculate the cyclist's average speed in m/s.
Explain whether the cyclist's speed and velocity are always the same during the journey.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) mass: kilogram (kg), distance: metre (m), average speed: metre/second (m/s), force: newton (N)
(b) 5.0 m/s
(c) No, speed is the rate of movement regardless of direction, but velocity also includes direction. If the cyclist changes direction (e.g., going up the hill), speed can stay the same but velocity changes; if returning or changing direction, velocity can be different even if speed is equal.
Common mistakes: Mixing up units such as using km/h; Using distance instead of displacement for velocity.
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Marking points
B1 (a) · 2 marks · 1 mark for any two correct SI units, 2 marks for all four correct.
M1 (b) · 1 mark · Method: uses v = s/t or equivalents, with s = 1500 m, t = 300 s.
A1 (b) · 1 mark · Correct evaluation: 5.0 m/s.
B2 (c) · 2 marks · 1 mark for stating speed and velocity can be different if direction changes; 1 mark for clear explanation about direction/displacement.
Worked solution
(a) The SI units are: mass: kilogram (kg), distance: metre (m), average speed: metre/second (m/s), force: newton (N).
(b) Average speed = distance / time = 1500 m / 300 s = 5.0 m/s.
(c) Speed is a scalar, only needing magnitude; velocity has magnitude and direction. If the cyclist changes direction or returns to the starting point, velocity changes even if speed remains constant; so, they are not always the same.