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

WJEC GCSE Additional Science Teacher’s Notes
9. Why is heat normally ‘wasted’ during an energy transfer
During energy transfers where heat is produced, the heat is normally lost into the surroundings,
and cannot be recovered.
10. Why are muscles only 25% efficient
75% of the energy produced in muscles is wasted as heat as the muscles contact and relax
11. How do our bodies deal with the heat produced by our muscles when we exercise
The excess heat is controlled via homeostasis by sweating, vasodilation of capillaries near the
surface of the skin and the flattening of skin hairs.
PRACTICAL How much work do you do (page 192)
Students need to measure the distances moved by the different weights (vertically) and calculate
the weights using weight = mg, or by direct measurement via a newton meter.
Students should take care measuring the distances to ensure that the rulers/tape measure/fingers
do not get caught in the machines.
If students are measuring forces directly with a newton meter, loops of string would be useful to
put round the machine handles so that the newton meters can be attached.
If students calculate the efficiency of each machine, a bar chart would be a suitable way of
illustrating the results.
_ Running with a rugby ball – analysing kinetic energy
(pages 193–94)
Questions
12. What is meant by kinetic energy
The energy possessed by a moving object.
13. What does the kinetic energy of a rugby player depend upon
Mass of object and velocity of object.
14. If a rugby player jogs at 5 m/s and then sprints at 10 m/s, she doubles her velocity. By what factor does
her kinetic energy increase
KE is proportional to v 2 , so if v doubles, KE goes up by a factor of 2 2 = 4.
15. At a recent Wales squad training session, the sprinting performance of various players was measured
and recorded. Table 17.1 summarises the findings of the fitness director. Copy and complete the table
(minus the photos), calculating the maximum kinetic energy of each player.
AlunWyn Jones: 4994 J
Shane Williams: 5018 J
Adam Jones: 4588 J
James Hook: 5029 J
16. A standard (size 5) rugby ball has a mass of 0.44 kg. When kicking from a tee, James Hook can kick
the ball with an initial velocity of 24.5 m/s. Calculate the initial kinetic energy of the ball.
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