Q296 · Practice questionTechnology-activeSimple familiar5 marks
QUESTION 296 (5 marks)
A channel has the depths in the supplied table, measured at equally spaced positions across its 4 m width. The water has uniform downstream speed 0.75 m/s. The flow rate equals cross-sectional area times downstream speed.
a)[3 marks]
Use Simpson's rule with four strips to estimate the cross-sectional area. Show the substituted ordinates.
b)[1 mark]
A worker estimates the flow rate as 2.5 m/s. Evaluate the estimate using your result.
c)[1 mark]
State one way to improve the area approximation using Simpson's rule.
WORKED SOLUTION
5 marksPractice marking scheme
ANSWER
(a) m. (b) The model gives about 3.1 m/s, so 2.5 is too low. (c) Measure depths at 0.5 m intervals and use eight strips.
Worked solution
(a) The strip width is 1 m. Thus m.
(b) m/s. The worker underestimates by 0.6 m/s under the stated uniform-speed model.
(c) A smaller strip width with additional measured ordinates resolves the shape more finely. Inventing midpoint depths from linear interpolation does not supply new measurement information; more strips do not guarantee improved accuracy for every possible profile.
Equivalent justified methods accepted; respect any requested proof method.
Exact values unless specified. Sketches assessed by mathematical features, not artistic quality.
Part a: Use width 1 and the correct Simpson weights.
Part a: Substitute all five ordinates in order.
Part a: Calculate area m.
Part b: Calculate 3.1 m/s and compare with the claim.
Part c: Propose finer equally spaced measurements with an even number of strips.
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