Congratulations to those of you who managed to
find the right answer.
Robyn from the Katherine Semar Junior School
was one of the first to send in a correct answer:
The shape is a pentagon, the radius is 30, the dot is on the middle
of the bottom left sloping edge.
Robert and Joel from Cowbridge
Comprehensive also sent in correct solutions.
Here is Robert's nice piece of detective
I already knew that the radius of the shape was 30.
The graph had four lines before it repeated, but since one was
twice as long as the others, the shape had to have five sides.
Since the speed was never zero, the dot could not have been on a
corner of the shape, but in the middle of a side.
Robert goes on to consider on which side of
the pentagon the dot must have been placed:
The speed of the dot would have been slowest as the side it
was on came onto and off the ground.
Since the line that marked the lowest speed (which was twice
as long as the others) was the last line before the graph repeated
itself, the dot had to be on the side that came off the ground
Therefore, the shape that made that graph was a pentagon, of radius
30, with the dot in the middle of the lower left side.
Thank you Cristina, from City of London
School for Girls, for sending us a very comprehensive