Forces and Motion
5 marks · EasyA cyclist rides a bike along a straight road. At one point, the cyclist stops at a traffic light for 20 s, then cycles away at a steady speed for the next 60 s.
Complete the table to show which of the following are scalar and which are vector quantities: speed, displacement, time, velocity.
| Quantity | Type (Scalar or Vector) |
|---|---|
| Speed | |
| Displacement | |
| Time | |
| Velocity |
State the SI units for (i) speed and (ii) time.
Explain the difference between speed and velocity.
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) — · must show Speed: scalar, Displacement: vector, Time: scalar, Velocity: vector
(b) (i) m/s, (ii) s · must show m/s, s
(c) Speed is the rate of change of distance and has no direction (scalar), while velocity is the rate of change of displacement and includes a direction (vector). · must show Speed: scalar, rate of distance, Velocity: vector, rate of displacement in a direction
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Any two quantities correctly classified as scalar or vector.
B1 (a) · 1 mark · Any two other quantities correctly classified as scalar or vector.
B1 (b) · 1 mark · Correct SI units given for both speed (m/s) and time (s).
B1 (c) · 1 mark · States that speed is scalar and velocity is vector or describes the difference in directionality.
B1 (c) · 1 mark · Explains that velocity involves displacement/direction, while speed does not.
Worked solution
| Quantity | Type (Scalar or Vector) |
|---|---|
| Speed | Scalar |
| Displacement | Vector |
| Time | Scalar |
| Velocity | Vector |
(i) The SI unit for speed is m/s. (ii) The SI unit for time is s.
Speed is a scalar quantity — it only has size (magnitude) and does not depend on direction. Velocity is a vector quantity — it has both magnitude and direction. For example, a car moving at 10 m/s north has a velocity of 10 m/s north but a speed of 10 m/s.