Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
b Plot a graph of Usain Bolt’s mean speed (on the y-axis) against distance (on the x-axis). Take
the mean speed to occur in the middle of each 10 m segment of the race, so plot the distances
as: 5 m, 15 m, 25 m and so on up to 95 m.
See graph under part (d) below.
c
Describe the pattern (or shape) of the graph and try to explain how mean speed varies with
distance.
The average speed increases from zero to about 10 m/s in a distance of 15 m – as Usain
was accelerating out and away from the blocks. After 15 m, the average speed increases
more slowly up to a maximum of just over 12 m/s for about 70 m – when Usain was
running at maximum speed. After this Usain slowed back to about 11 m/s for the last 15
m – as he was lunging for the line.
d In 2009, the Cincinnati Zoo’s 8-year-old female cheetah Sarah became the world’s fastest land
mammal. Sarah covered 100 m in a time of 6.13 seconds, breaking the previous mark of 6.19
seconds set by a male South African cheetah named Nyana in 2001. Use this information
(assuming that a cheetah will have a similar pattern of running to Usain Bolt) to sketch on the
same graph the pattern for Sarah compared with Usain Bolt.
Sarah the cheetah
Usain Bolt
Discussion points
1. You can find lots of videos of Usain Bolt’s 2008 Olympic 100 m final online. Watch the race. It
almost feels as if he is slowing down at the end and waving to the crowd, yet in reality he’s still
running at top speed. How much faster do you think human beings can run Is there going to be an
ultimate ‘top speed’ or do you think that humans will get progressively quicker and quicker
Many suitable links are available on youtube.com. Some interesting views on how fast a
human being can run are available from Peter Weyand from Southern Methodist University,
USA:
http://smu.edu/education/APW/LocomotorNews.asp
2. The cheetah has a substantially faster top speed than most of its prey (for example the springbok),
yet it only has a 50% kill success rate. Why do you think that half of the cheetah’s prey get away
Cheetahs can reach a speed approaching 70 mph (110 km/h), however this speed can be
maintained for only a few hundred metres or for about one minute. If it is forced to run
longer than a minute, it usually gives up the chase.
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