Q19 · 2020 · Technology-activeComplex unfamiliar7 marks
QUESTION 19 (7 marks)
Consider the following information when completing this question. The length of a curve over the interval is You are driving along a road with a vertical distance above sea level (in metres) given by the function where is the horizontal distance from an initial point of measurement (in kilometres) at sea level. Assume that if is positive you are east of the initial point of measurement and if is negative you are west of the initial point of measurement. You start your drive along the road at a horizontal distance of 10 kilometres west of the initial point of measurement and drive until you are at a horizontal distance of 10 kilometres east of the initial point. Determine the time you spend driving downhill, if you drive downhill at an average speed of 40 km/h.
WORKED SOLUTION
7 marksQCAA guide · typeset solution
ANSWER
approximately hours
Worked solution
Downhill driving corresponds to where . Graphing shows the function is decreasing for . The downhill distance is Therefore The official marking guide notes that an erroneous answer of 0.33 hours, corresponding to 13.25 km, was awarded full marks where students failed to ensure and were measured in the same units, because the curve-length formula was unfamiliar.
correctly identifies values of associated with downhill drive
correctly uses an appropriate mathematical representation
determines decreasing interval
establishes integral expression for the total distance travelled downhill
determines the distance travelled downhill
determines time travelling downhill
shows logical organisation communicating key steps
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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