Date | May 2021 | Marks available | 4 | Reference code | 21M.2.AHL.TZ1.4 |
Level | Additional Higher Level | Paper | Paper 2 | Time zone | Time zone 1 |
Command term | Write down | Question number | 4 | Adapted from | N/A |
Question
Charlotte decides to model the shape of a cupcake to calculate its volume.
From rotating a photograph of her cupcake she estimates that its cross-section passes through the points and , where all units are in centimetres. The cross-section is symmetrical in the -axis, as shown below:
She models the section from to as a straight line.
Charlotte models the section of the cupcake that passes through the points and with a quadratic curve.
Charlotte thinks that a quadratic with a maximum point at and that passes through the point would be a better fit.
Believing this to be a better model for her cupcake, Charlotte finds the volume of revolution about the -axis to estimate the volume of the cupcake.
Find the equation of the line passing through these two points.
Find the equation of the least squares regression quadratic curve for these four points.
By considering the gradient of this curve when , explain why it may not be a good model.
Find the equation of the new model.
Write down an expression for her estimate of the volume as a sum of two integrals.
Find the value of Charlotte’s estimate.
Markscheme
A1A1
Note: Award A1 for , A1 for .
Award a maximum of A0A1 if not part of an equation.
[2 marks]
(M1)A1
[2 marks]
gradient of curve is positive at R1
Note: Accept a sensible rationale that refers to the gradient.
[1 mark]
METHOD 1
let
differentiating or using (M1)
substituting in the coordinates
(A1)
(A1)
solve to get
OR A1
Note: Use of quadratic regression with points using the symmetry of the graph is a valid method.
METHOD 2
(M1)
(M1)
(A1)
OR A1
[4 marks]
(M1)(M1) (M1)A1
Note: Award (M1)(M1)(M1)A0 if is omitted but response is otherwise correct. Award (M1) for an integral that indicates volume, (M1) for their part (a) within their volume integral, (M1) for their part (b)(i) within their volume integral, A1 for their correct two integrals with all correct limits.
[4 marks]
A1
[1 mark]