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GCSE Questions: Energy Changes

Q7. A scientist investigated how the maximum muscle power of humans varies with age and gender.

The scientist asked volunteers to stand on a platform and to jump as high as they could.

The diagram shows a volunteer taking part in the experiment.

An electronic timer measured the time that the volunteer was in the air.

 

(a) The muscle power in watts per kg is calculated using the following equation:

muscle power = 9.8 × jump height/time

One volunteer has a muscle power of 41 W/kg. He was in the air for 0.12 s

Calculate his jump height.

41 = 9.8 x h/0.12

h = 41 x 0.12/9.8

h = 0.50 m

[3 marks]

(b) Write down the equation which links kinetic energy, mass and speed.

kinetic energy = 0.5 × mass × (speed)2

or

Ek = ½ mv2

[1 mark]

(c) One volunteer had a kinetic energy of 270 J and a speed of 3.0 m/s at the moment he left the ground. Calculate his mass.

270 = ½ m x 3.02

m = 270 x 2/9

m = 60 kg

[3 marks]

(d) The graph below shows the scientist's results.

Compare the muscle power of males with the muscle power of females.

Use data from the graph in your answer.

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 2:

Scientifically relevant features are identified; the way(s) in which they are similar / different is made clear.
3 - 4 marks
Level 1:

Relevant features are identified and differences noted.
1 - 2 marks
Level 0:

No relevant information
0 marks

 

Examples of physics points that should be made in the response:

males have a greater muscle power than females for most of their lives

males have a greater muscle power than females above 9/10 years old

males have a lower muscle power than females below 9/10 years old

there is a similar pattern for males and females as age increases

males have a peak muscle power at 25 years old whereas females have a peak muscle power at 20/21 years old

at 9/10 years old males have the same muscle power as females

peak muscle power for males (47 W/kg) is greater than peak muscle power for females (37 W/kg)

the rate of increase of muscle power is greater for males than females (between 5 and 25 years old)

the rate of decrease of muscle power is greater for males than females. Ignore comments relating to strength

[4 marks]

(e) The muscle power of each volunteer was measured five times. The highest muscle power reading was recorded instead of calculating an average. Suggest one reason why.

Any 1 from:

maximum height reached is a better indicator of maximum muscle power

maximum / peak muscle power was being investigated, not mean / average muscle power

volunteer may not use maximum effort on the first try

performance may improve with practise

performance may get worse with tiredness

[1 mark]

[Total 12 marks]