Q19 · 2020 · Technology-freeComplex unfamiliar7 marks
QUESTION 19 (7 marks)
A circular-based bowl has been positioned symmetrically on a Cartesian plane as shown in the diagram. The bowl has a shape that can be generated by rotating the curve about the -axis for cm. The bowl is being filled with a liquid at the rate of cm s. Determine the rate at which the depth of liquid is increasing when the depth of liquid reaches one-third of the height of the bowl.
WORKED SOLUTION
7 marksQCAA guide · typeset solution
ANSWER
cm s.
Worked solution
Rearranging gives . If the liquid depth is ,
so . Since and ,
The bowl height is cm, hence the required depth is cm. Therefore cm s.
correctly expresses as the subject of the given relationship
establishes volume of bowl as a definite integral
determines an expression for
uses a related rate of change equation to determine a relationship between and
correctly determines the instantaneous depth of liquid for the required calculation
determines the required rate
shows logical organisation communicating key steps
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