Question 1

Paper 1Medium14 marks

An engineer records the water height, hh cm, in a reservoir while a pump fills it. The pump remains on throughout a planned 8-minute run, and there is no outlet. The measurements shown in Figure 1 were taken during the first 5 minutes. Heights are recorded to the nearest 0.10.1 cm.

012345678051015202530t (minutes)h (cm)(0, 3.8)(1, 10.3)(2, 15.6)(3, 20.0)(4, 23.1)(5, 25.0)
(a)

Using the shape of the data in Figure 1, choose a linear or quadratic model for hh in terms of tt Justify your choice.

[2]
(b)

Let h=at2+bt+ch=at^2+bt+c Using the measurements at t=0t=0 t=2t=2 and t=4t=4 show that a fitted model is

h=−0.5375t2+6.975t+3.8.h=-0.5375t^2+6.975t+3.8.
[4]
(c)

Hence, using this model, determine the first time during the 5-minute measurement interval at which the model predicts h=25.0h=25.0 cm. Give your answer to the nearest 0.010.01 minute.

[3]
(d)

At t=3t=3 compare the model’s predicted height with the recorded height. State what this comparison suggests about the model’s fit at that time.

[2]
(e)

Use the fitted model to predict the height after 8 minutes. State whether this prediction should be considered reliable, giving two reasons.

[3]

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