Date | May 2022 | Marks available | 1 | Reference code | 22M.1.AHL.TZ2.17 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 2 |
Command term | Show that and Hence | Question number | 17 | Adapted from | N/A |
Question
The cross-section of a beach is modelled by the equation y=0.02x2 for 0≤x≤10 where y is the height of the beach (in metres) at a horizontal distance x metres from an origin. t is the time in hours after low tide.
At t=0 the water is at the point (0, 0). The height of the water rises at a rate of 0.2 metres per hour. The point W(x(t), y(t)) indicates where the water level meets the beach at time t.
A snail is modelled as a single point. At t=0 it is positioned at (1, 0.02). The snail travels away from the incoming water at a speed of 1 metre per hour in the direction along the curve of the cross-section of the beach. The following diagram shows this for a value of t, such that t>0.
When W has an x-coordinate equal to 1, find the horizontal component of the velocity of W.
Find the time taken for the snail to reach the point (10, 2).
Hence show that the snail reaches the point (10, 2) before the water does.
Markscheme
use of chain rule (M1)
dydt=dydxdxdt
attempt to find dydx at x=1 (M1)
0.2=0.04×dxdt
(dxdt=) 5 A1
[3 marks]
if the position of the snail is
from part (a)
since speed is :
finding modulus of velocity vector and equating to (M1)
OR
OR
OR (A1)
OR (M1)
hours A1
[4 marks]
EITHER
time for water to reach top is hours (seen anywhere) A1
OR
or at time , height of water is A1
THEN
so the water will not reach the snail AG
[1 mark]
Examiners report
In part (a), a small minority of candidates found the horizontal component of velocity correctly. Few candidates made any significant progress in part (b).