5.4 Investigating reaction time
7 exam questions worth 15 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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A student investigates whether drinking cola affects reaction time, using the ruler-drop test.
Identify the independent variable, the dependent variable and one control variable.
Mark scheme
- independent: whether cola was drunk / amount of caffeine (1)
- dependent: reaction time / distance the ruler falls (1)
- control: any one from: same catcher / same ruler / same starting position of fingers / same hand / same person dropping / same time after the drink / same volume of drink (1)
Model answer
The independent variable is whether the student has drunk cola. The dependent variable is the reaction time, measured as the distance the ruler falls. A control variable is using the same hand to catch the ruler each time.
Explain why the person dropping the ruler should not warn the catcher before letting go.
Mark scheme
(otherwise) the catcher could anticipate / predict the drop, so it would not measure their true reaction time
Model answer
If the catcher knows when it is coming they can anticipate it, so the result would not measure their real reaction time.
Five catches gave these distances: 21 cm, 19 cm, 35 cm, 20 cm, 22 cm.
Identify the anomalous result, then calculate the mean distance without it.
Mark scheme
- anomaly is 35 (cm) (1)
- (21 + 19 + 20 + 22) ÷ 4 (1)
- = 20.5 (cm) (1)
- allow 20.5 for 3 marks with no working if 35 identified
Model answer
The anomaly is 35 cm because it is far from the others. Mean = (21 + 19 + 20 + 22) ÷ 4 = 82 ÷ 4 = 20.5 cm.
Reaction time can be calculated with the equation:
where d is the distance fallen in metres and g = 9.8 m/s².
A ruler falls 0.12 m before it is caught. Calculate the reaction time. Give your answer to 2 significant figures.
Mark scheme
- t = √(2 × 0.12 ÷ 9.8) = √0.02449 (1)
- = 0.16 (s) (1)
Model answer
t = √(2 × 0.12 ÷ 9.8) = √0.0245 = 0.156... = 0.16 s
During the investigation the student's reaction times got shorter with each catch.
Suggest why, and suggest how the method could be improved to stop this affecting the results.
Mark scheme
- the student was getting practice / learning (1)
- do practice catches before recording / alternate the conditions / give a rest between catches (1)
Model answer
The student was improving with practice. They should do several practice catches before recording any results, or alternate between the two conditions so practice affects both equally.
Give two advantages of using a computer reaction-time test instead of the ruler-drop test.
Mark scheme
Any two from:
- more precise / measures to the millisecond (1)
- measures time directly / no conversion needed (1)
- removes human error in dropping or reading the ruler (1)
- the stimulus appears at random so it cannot be anticipated (1)
Model answer
It measures reaction time directly to the nearest millisecond, so it is more precise, and it removes human errors such as reading the ruler or giving away when it will be dropped.
Explain why catching a falling ruler is not a reflex action.
Mark scheme
- it involves the conscious part of the brain / a decision is made (1)
- reflexes are automatic / do not involve the conscious brain (1)
Model answer
Catching the ruler involves the conscious part of the brain deciding to respond, whereas a reflex is automatic and does not involve conscious thought.
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