The difference between speed and velocity
4 marks · HardThe velocity–time graph below shows the motion of a motorbike travelling in a straight line for 12 s. Use this information to answer the questions.
Describe the motion of the motorbike from 0 to 2 seconds, and from 2 to 6 seconds.
Calculate the acceleration of the motorbike from 6 to 10 seconds.
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) 0–2 s: The motorbike accelerates from rest to 4 m/s. 2–6 s: It travels at constant velocity (4 m/s).
(b) -1.5 m/s^2
Common mistakes: Incorrectly describing constant velocity as acceleration; Getting velocity change or time interval wrong in calculation; Omitting negative sign in acceleration
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States correctly that the motorbike accelerates from 0 m/s to 4 m/s in the first 2 seconds.
B2 (a) · 1 mark · States correctly that the motorbike moves at constant velocity (4 m/s) from 2 s to 6 s.
M1 (b) · 1 mark · Substitutes correct values into acceleration formula: (v-u)/t, using v = -2 m/s, u = 4 m/s, t = 4 s.
A1 (b) · 1 mark · Obtains correct answer: -1.5 m/s^2. (follow-through)
Worked solution
a) From 0 to 2 seconds: The graph rises steeply from 0 to 4 m/s — the motorbike is accelerating from rest. From 2 to 6 seconds: The line is flat at 4 m/s — the motorbike travels at constant velocity.
b) Use a = (v-u)/t. From 6 to 10 s: Initial velocity u = 4 m/s, final velocity v = -2 m/s, t = 4 s.