Question 28
A lorry travels at a
constant speed and then decelerates until it stops.
Which graph shows the variation with time of
the distance travelled by the lorry?
Reference: Past Exam Paper – November 2016 Paper 12 Q7
Solution:
Answer:
B.
The gradient of a
distance-time graph gives the speed of the lorry.
The lorry first travels at
constant speed. So, the gradient should be constant at first. That is, it
should be a straight line. [A incorrect]
A horizontal line means
that the gradient and hence, the speed is zero. This cannot be correct as the
lorry IS moving at constant speed. [C incorrect]
The lorry then decelerates
until it stops. That is, its speed decreases until it becomes zero. In the
graph, the gradient should decrease until it becomes a horizontal line (speed =
0). [B is correct]
Recall that the gradient
of the distance-time graph gives the speed. Speed is a scalar quantity, and it
makes no sense to have a negative speed as indicated by the gradient of graph
D. [D is incorrect]
Also, as the lorry moves, the distance travelled (a scalar quantity) should increase. It cannot decrease since this is not ‘displacement’.
No comments:
Post a Comment
If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation