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Calculus — Free Maths AA SL Practice Questions

1FoundationSAQ-SDefinition and calculation of limits5 marksPaper 1~8 min
Consider the function g(x)={2x+1,x<25,x=2x23,x>2g(x) = \begin{cases} 2x + 1, & x < 2 \\ 5, & x = 2 \\ x^2 - 3, & x > 2 \end{cases}
(a)
Determine limx2g(x)\lim_{x \to 2^-} g(x) and limx2+g(x)\lim_{x \to 2^+} g(x)[2 marks]
(b)
State whether limx2g(x)\lim_{x \to 2} g(x) exists, justifying your answer. [1 mark]
(c)
Determine whether gg is continuous at x=2x = 2. Justify your answer fully. [2 marks]
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2MasterySAQ-SDefinition and calculation of limits5 marksPaper 1~8 min
Consider the function f(x)=x24x2f(x) = \dfrac{x^2 - 4}{x - 2} for x2x \neq 2.
(a)
Show that limx2f(x)=4\displaystyle\lim_{x \to 2} f(x) = 4[2 marks]
(b)
Define g(x)=x24x24g(x) = \dfrac{x^2 - 4}{x - 2} - 4 for x2x \neq 2. Show that g(x)=x2g(x) = x - 2, and hence calculate limx2g(x)x2\displaystyle\lim_{x \to 2} \dfrac{g(x)}{x - 2}[2 marks]
(c)
The result in (b) equals f(2)f'(2), the derivative of ff at x=2x = 2, computed from first principles. Explain why this the case, and state the value of f(2)f'(2)[1 mark]
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3ChallengeSAQ-LDefinition and calculation of limits8 marksPaper 1~12 min
A function gg is defined by g(x)=x24x2g(x) = \dfrac{x^2 - 4}{|x-2|} for xRx \in \mathbb{R}, x2x \neq 2.
(a)
Show that g(x)=x+2g(x) = x + 2 for x>2x > 2 and g(x)=(x+2)g(x) = -(x+2) for x<2x < 2[2 marks]
(b)
Hence determine limx2+g(x)\lim_{x \to 2^+} g(x) and limx2g(x)\lim_{x \to 2^-} g(x), and state whether gg has a removable discontinuity at x=2x = 2. Justify your answer. [3 marks]
(c)
Using your results from (a), write down the equations of the oblique asymptotes of the graph of gg. Hence sketch the graph of gg, clearly labelling the asymptotes, the behaviour near x=2x = 2, and the yy-intercept. [3 marks]
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4FoundationSAQ-SDefinition and calculation of limits5 marksPaper 1~8 min
Consider the function f(x)=x21x1f(x) = \dfrac{x^2 - 1}{x - 1}, for x1x \neq 1.
(a)
Find limx1f(x)\lim_{x \to 1} f(x)[2 marks]
(b)
Hence, state the value of f(1)f(1) that would make ff continuous at x=1x = 1[1 mark]
(c)
The function gg is defined as g(x)={x21x1,x1k,x=1g(x) = \begin{cases} \dfrac{x^2 - 1}{x - 1}, & x \neq 1 \\[6pt] k, & x = 1 \end{cases} Determine the value of kk for which gg is continuous at x=1x = 1, and state whether g(x)=x+1g(x) = x + 1 for all xRx \in \mathbb{R}. Justify your answer. [2 marks]
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5MasterySAQ-SDefinition and calculation of limits5 marksPaper 1~8 min
The function ff is defined by f(x)=3x1f(x) = \dfrac{3}{x-1}, for x1x \neq 1.
(a)
Explain why limx1+f(x)=+\displaystyle\lim_{x \to 1^+} f(x) = +\infty[2 marks]
(b)
Write down limx1f(x)\displaystyle\lim_{x \to 1^-} f(x)[1 mark]
(c)
A student claims that because both one-sided limits of ff at x=1x = 1 are infinite, the two-sided limit limx1f(x)\displaystyle\lim_{x \to 1} f(x) exists and equals ++\infty. Determine whether the two-sided limit exists and evaluate the student's claim. [2 marks]
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6FoundationSAQ-SDefinition of a derivative (rate of change)5 marksPaper 1~8 min
The graph of y=f(x)y = f(x) for 2x4-2 \leq x \leq 4 is shown below. The tangent to the curve at point PP, where x=1x = 1, is also drawn.
(a)
State the geometric meaning of f(1)f'(1)[1 mark]
(b)
Find the value of f(1)f'(1)[2 marks]
(c)
The normal to the curve at PP intersects the xx-axis at point QQ. Find the coordinates of QQ[2 marks]
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7MasterySAQ-SDefinition of a derivative (rate of change)8 marksPaper 1~12 min
A water tank has a small hole at its base. The volume of water, VV litres, remaining in the tank tt minutes after the hole is unplugged is given by V(t)=100(1t20)2,0t20.V(t) = 100\left(1 - \frac{t}{20}\right)^2, \quad 0 \leq t \leq 20.
(a)
Show that the rate of change of volume is V(t)=10(1t20)V'(t) = -10\left(1 - \dfrac{t}{20}\right)[3 marks]
(b)
Find the time at which the water is draining at a rate of 55 litres per minute. [2 marks]
(c)
The average rate of change of volume over the entire interval 0t200 \leq t \leq 20 is compared with the instaneous rate found in part (b). Determine the average rate of change of VV over [0,20][0, 20] and explain why it is consistent with the answer to part (b). [3 marks]
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8ChallengeSAQ-LDefinition of a derivative (rate of change)8 marksPaper 1~12 min
A particle moves along a straight line such that its displacement, ss metres, from a fixed point OO at time tt seconds is given by s(t)=t36t2+9t+2,t0.s(t) = t^3 - 6t^2 + 9t + 2, \quad t \geq 0.
(a)
Using the definition of the derivative as a limit, f(x)=limh0f(x+h)f(x)h,f'(x) = \lim_{h \to 0} \frac{f(x+h)-f(x)}{h}, show that the velocity of the particle is v(t)=3t212t+9v(t) = 3t^2 - 12t + 9[4 marks]
(b)
Determine the values of tt at which the particle is instaneously at rest. [2 marks]
(c)
Determine the intervals within 0t40 \leq t \leq 4 during which the particle moves in the positive direction and the intervals during which it moves in the negative direction. [1 mark]
(d)
Hence determine the total distance travelled by the particle in the first 44 seconds. [1 mark]
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9FoundationSAQ-SRules of differentiation (power, product, quotient, chain rule)s5 marksPaper 1~8 min
A company models the profit P(x)P(x), in thousands of dollars, from selling xx hundred units of a product as P(x)=(2x+3)(x1)2,x1.P(x) = (2x + 3)(x - 1)^2, \quad x \geq 1. -
(a)
Find P(x)P'(x). Write your answer in the form P(x)=2(x1)(ax+b)P'(x) = 2(x-1)(ax + b), where aa and bb are integers. - [3 marks]
(b)
Find the value of xx for which P(x)=0P'(x) = 0 and x>1x > 1, or state that no such value exists. Justify your answer. - [1 mark]
(c)
The company considers increasing production beyond the level found in (b). Using your results from (a) and (b), determine whether profit is increasing or decreasing for x>1x > 1, and interpret what this means for the company. [1 mark]
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10MasterySAQ-SDefinition of a derivative (rate of change)7 marksPaper 1~11 min
The graph of a function ff is shown below. The points A(1,2)A(1,\,2) and B(4,8)B(4,\,8) lie on the curve y=f(x)y = f(x). The tangent to the curve at AA has equation y=3x1y = 3x - 1.
(a)
Show that the gradient of the chord ABAB is 22[2 marks]
(b)
State the two conditions on ff required for the Mean Value Theorem to apply on the interval [1,4][1,\,4][1 mark]
(c)
Hence, using the Mean Value Theorem, deduce that there exists a point c(1,4)c \in (1,\,4) such that f(c)=2f'(c) = 2[2 marks]
(d)
The tangent at AA has gradient 33. Explain why the Mean Value Theorem cannot be used on the interval [1,4][1,\,4] to guarantee the existence of a point where f=3f' = 3[2 marks]
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11FoundationSAQ-SIndefinite integrals and their propertiess5 marksPaper 1~8 min
A particle moves along a straight line such that its velocity vm s1v\,\text{m s}^{-1} at time tt seconds is given by v(t)=3t24t+5v(t) = 3t^2 - 4t + 5.
(a)
Find an expression for the displacement s(t)s(t), given that s(0)=2s(0) = 2[3 marks]
(b)
Determine whether the particle is moving away from or towards its initial position at t=3t = 3 seconds. Justify your answer. [2 marks]
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12MasterySAQ-SIndefinite integrals and their propertiess5 marksPaper 1~8 min
A particle moves along a straight line such that its velocity vm s1v\,\text{m s}^{-1} at time tt seconds is given by v(t)=3t212t+9v(t) = 3t^2 - 12t + 9, for t0t \geq 0.
(a)
Show that the displacement s(t)ms(t)\,\text{m} of the particle from its starting point is given by s(t)=t36t2+9ts(t) = t^3 - 6t^2 + 9t[2 marks]
(b)
Hence find the total distance travelled by the particle in the first 44 seconds. [3 marks]
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13ChallengeSAQ-LIndefinite integrals and their propertiess8 marksPaper 1~12 min
A manufacturer produces a decorative rod whose cross-sectional area (in cm2\text{cm}^2) at distance xx metres from one end is given by A(x)=4xe2x+3A(x) = 4xe^{-2x} + 3, for 0x30 \leq x \leq 3.
(a)
Determine A(x)dx\displaystyle\int A(x)\,dx[4 marks]
(b)
Hence find the exact volume of the rod in cm3\text{cm}^3[2 marks]
(c)
A second rod of the same length has cross-sectional area B(x)=4xe2x+kB(x) = 4xe^{-2x} + k, where kk is a positive constant. The volume of the second rod is exactly 12cm312\,\text{cm}^3. Determine the exact value of kk and hence deduce what geometric feature of the two rods differs. [2 marks]
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14FoundationSAQ-SIndefinite integrals and their propertiess5 marksPaper 1~8 min
Consider the function f(x)=1x2f(x) = \dfrac{1}{x^2} for x>0x > 0.
(a)
Find f(x)dx\displaystyle\int f(x)\,dx[2 marks]
(b)
The graph of F(x)F(x), antiderivative of f(x)f(x), passes through the point (1,3)(1,\,3). Find F(x)F(x)[2 marks]
(c)
Hence find the value of xx for which F(x)=3.5F(x) = 3.5[1 mark]
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15MasterySAQ-SIndefinite integrals and their propertiess5 marksPaper 1~8 min
Consider the function f(x)=12(2x+1)2f(x) = \dfrac{12}{(2x+1)^2}, for x>12x > -\dfrac{1}{2}.
(a)
Show that f(x)dx=62x+1+C\displaystyle\int f(x)\,dx = -\frac{6}{2x+1} + C[2 marks]
(b)
The graph of y=f(x)y = f(x) passes through the point PP where x=1x = 1. The tangent to the curve at PP intersects the xx-axis at point QQ. Find the xx-coordinate of QQ[3 marks]
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16FoundationSAQ-SSolving first-order differential equationss7 marksPaper 1~11 min
The number of bacteria, NN, in a culture grows at a rate proportional to NN. This modelled by the differential equation dNdt=kN\dfrac{dN}{dt} = kN, where tt is the time in hours and kk is a positive constant.
(a)
Show that the general solution to dNdt=kN\dfrac{dN}{dt} = kN is N=AektN = Ae^{kt}, where AA is a positive constant. [2 marks]
(b)
Initially there are 500500 bacteria. After 33 hours there are 40004000 bacteria. Find the exact value of kk[3 marks]
(c)
A scientist claims the culture will exceed 5000050\,000 bacteria within 1010 hours of the start. Determine whether this claim is correct. [2 marks]
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17MasterySAQ-SSolving first-order differential equationss5 marksPaper 1~8 min
The population of a colony of ants is modelled by the differential equation dPdt=150P(500P)\frac{dP}{dt} = \frac{1}{50}P(500 - P) where PP is the population at time tt years, t0t \geq 0. Initially, the population is 100100 ants.
(a)
Show that 1P(500P)=1500(1P+1500P)\frac{1}{P(500-P)} = \frac{1}{500}\left(\frac{1}{P} + \frac{1}{500-P}\right) [2 marks]
(b)
Hence solve the differential equation, giving your answer in the form P=a1+bectP = \frac{a}{1 + be^{-ct}} where aa, bb, cc are integers. [3 marks]
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18ChallengeSAQ-LSolving first-order differential equationss8 marksPaper 1~12 min
A cylindrical water tank has a constant cross-sectional area of 2m22\,\text{m}^2 and a small hole at its base. Water leaks such that the rate of change of volume VV (in m3\text{m}^3) at time tt (in hours) is proportional to the square root of the depth hh (in metres). The tank is initially full with depth 4m4\,\text{m}. After 11 hour, the depth has decreased to 3m3\,\text{m}. Using V=2hV = 2h, the differential equation for the depth is dhdt=kh,k>0.\frac{dh}{dt} = -k\sqrt{h}, \quad k > 0.
(a)
Show that k=2(23)k = 2(2 - \sqrt{3})[4 marks]
(b)
Determine the time TT at which the depth reaches 2m2\,\text{m}. Give your answer in exact form. [2 marks]
(c)
Determine whether the tank empties completely according to this model. Justify your answer mathematically. [2 marks]
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19FoundationSAQ-SSolving first-order differential equationss7 marksPaper 1~11 min
Consider the differential equation dydx=3x2y\dfrac{dy}{dx} = \dfrac{3x^2}{y}, where y>0y > 0.
(a)
Show that the general solution can be written as y2=2x3+Cy^2 = 2x^3 + C, where CC is a constant. [3 marks]
(b)
Given that y=3y = 3 when x=2x = 2, find the value of CC[1 mark]
(c)
Hence find the value of xx when y=5y = 5, giving your answer correct to 3 significant figures. [3 marks]
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20MasterySAQ-SSolving first-order differential equationss7 marksPaper 1~11 min
A chemical reaction is modelled by the differential equation dxdt=k(10x)(5x)\frac{dx}{dt} = k(10 - x)(5 - x) where xx grams is the amount of product formed after tt minutes and kk is a positive constant. Initially, x=0x = 0.
(a)
Show that 1(10x)(5x)=15(15x110x)\frac{1}{(10-x)(5-x)} = \frac{1}{5}\left(\frac{1}{5-x} - \frac{1}{10-x}\right) [2 marks]
(b)
Hence find an expression for xx in terms of tt and kk[3 marks]
(c)
State the value that xx approaches as tt \to \infty and explain why this consistent with the differential equation. [2 marks]
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21MasterySAQ-SDefinition and calculation of limits6 marksPaper 2~9 min
(a)
State the value of limx2h(x)\lim_{x \to -2^{-}} h(x)[1 mark]
(b)
State the value of limx+h(x)\lim_{x \to +\infty} h(x)[1 mark]
(c)
Determine whether limx1h(x)\lim_{x \to 1} h(x) exists. If it does, state its value. [2 marks]
(d)
Given that h(1)=4h(1) = 4, determine whether hh is continuous at x=1x = 1. Justify your answer. [2 marks]
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22MasterySAQ-SDefinition and calculation of limits6 marksPaper 2~9 min
The function ff is defined by f(x)=x22x3x29f(x) = \dfrac{x^2 - 2x - 3}{x^2 - 9}, for x±3x \neq \pm 3.
(a)
Calculate limx3f(x)\displaystyle\lim_{x \to 3} f(x)[3 marks]
(b)
Show that limx3f(x)\displaystyle\lim_{x \to -3} f(x) does not exist by evaluating limx3f(x)\displaystyle\lim_{x \to -3^-} f(x) and limx3+f(x)\displaystyle\lim_{x \to -3^+} f(x)[2 marks]
(c)
Hence classify each discontinuity of ff at x=3x = 3 and x=3x = -3, and state the equation of any asymptote arising from these discontinuities. [1 mark]
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23MasterySAQ-SDefinition and calculation of limits6 marksPaper 2~9 min
The graph of a function hh is shown below. The function has vertical asymptotes at x=2x = -2 and x=2x = 2, and a horizontal asymptote at y=1y = 1. Using the graph, determine the value of each of the following limits. If a limit does not exist, state this clearly.
(a)
limxh(x)\displaystyle\lim_{x \to -\infty} h(x) [1 mark]
(b)
limx2h(x)\displaystyle\lim_{x \to 2^-} h(x) [1 mark]
(c)
limx2h(x)\displaystyle\lim_{x \to -2} h(x) [2 marks]
(d)
limx2+h(x)\displaystyle\lim_{x \to 2^+} h(x) [1] (e) Hence, determine whether limx2h(x)\displaystyle\lim_{x \to 2} h(x) exists. Justify your answer. [1 mark]
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24MasterySAQ-SDefinition and calculation of limits6 marksPaper 2~9 min
A function is defined as f(x)=2x25x3x3f(x) = \dfrac{2x^2 - 5x - 3}{x - 3} for x3x \neq 3.
(a)
Show that limx3f(x)=7\displaystyle\lim_{x \to 3} f(x) = 7[3 marks]
(b)
A second function is defined as h(x)={f(x)x3ax22x=3h(x) = \begin{cases} f(x) & x \neq 3 \\ ax^2 - 2 & x = 3 \end{cases} where aa is a constant. Determine the value of aa such that hh is continuous at x=3x = 3, and hence state the value of h(3)h(3)[3 marks]
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25MasterySAQ-SDefinition and calculation of limits6 marksPaper 2~9 min
The graph of a function y=p(x)y = p(x) is shown below.
(a)
Calculate limx1p(x)\displaystyle\lim_{x \to -1} p(x)[2 marks]
(b)
Write down p(1)p(-1) and p(2)p(2)[2 marks]
(c)
The three conditions for continuity of a function ff at x=ax = a are: - f(a)f(a) is defined, - limxaf(x)\displaystyle\lim_{x \to a} f(x) exists, - limxaf(x)=f(a)\displaystyle\lim_{x \to a} f(x) = f(a). Determine, with justification, whether pp is continuous at x=1x = -1 and at x=2x = 2[2 marks]
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26MasterySAQ-SDefinition of a derivative (rate of change)6 marksPaper 2~9 min
The graph of f(x)=x36x2+9x+1f(x) = x^3 - 6x^2 + 9x + 1 is shown below for 0x40 \leq x \leq 4.
(a)
Show that the point A(2,3)A(2,\,3) lies on the curve ff[1 mark]
(b)
Find the exact gradient of the tangent to ff at x=2x = 2[3 marks]
(c)
The tangent to ff at AA intersects ff again at a point BB. Find the xx-coordinate of BB[2 marks]
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27MasterySAQ-SDefinition of a derivative (rate of change)6 marksPaper 2~9 min
The function f(x)=1xf(x) = \dfrac{1}{x} is defined for x>0x > 0. The graph of ff passes through points P(1,1)P(1,1) and Q(2,0.5)Q(2, 0.5).
(a)
Calculate the gradient of the secant line through PP and QQ[2 marks]
(b)
Calculate the gradient of the tangent to ff at PP, using differentiation. [2 marks]
(c)
The secant gradient found in part (a) is used as an approximation to the tangent gradient found in part (b). A second secant is drawn through PP and the point R ⁣(1.5,f(1.5))R\!\left(1.5,\, f(1.5)\right). Determine the gradient of this second secant and explain, with reference to your results, why moving QQ closer to PP along the curve gives a better approximation to the tangent gradient at PP[2 marks]
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28MasterySAQ-SDefinition of a derivative (rate of change)8 marksPaper 2~12 min
The volume VV of water in a cylindrical tank, measured in litres, is given by V(t)=2000+120t3t2V(t) = 2000 + 120t - 3t^2, where tt is the time in minutes after a valve is opened.
(a)
Calculate the rate at which the volume of water is changing at t=5t = 5 minutes. [3 marks]
(b)
Determine the time at which the volume of water is at its maximum. [2 marks]
(c)
Calculate the maximum volume of water in the tank and explain what happens to the volume for t>20t > 20[3 marks]
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29MasterySAQ-SDefinition of a derivative (rate of change)6 marksPaper 2~9 min
The height hh metres of a ball thrown vertically upwards from ground level is given by h(t)=24t4.9t2h(t) = 24t - 4.9t^2, where tt is the time in seconds after release.
(a)
Calculate the velocity of the ball at t=2t = 2 seconds. [2 marks]
(b)
Determine the time at which the ball reaches its maximum height. [2 marks]
(c)
A second ball is thrown vertically upwards from a platform 5m5\,\text{m} above ground level at the same instant, with the same initial speed. Its height above ground is modelled by g(t)=5+24t4.9t2g(t) = 5 + 24t - 4.9t^2. Determine whether the two balls reach their maximum heights at the same time, and calculate the difference in their maximum heights. [2 marks]
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30MasterySAQ-SDefinition of a derivative (rate of change)8 marksPaper 2~12 min
The population PP of a town, measured in thousands, is modelled by P(t)=50+8t0.2t2P(t) = 50 + 8t - 0.2t^2, where tt is the number of years after the year 2000.
(a)
Calculate the rate of change of the population in the year 2010. [3 marks]
(b)
Determine the year in which the population stops increasing. [2 marks]
(c)
A town planner claims that the population will exceed 130000130\,000 at some point. Determine whether this claim is correct, justifying your answer. [3 marks]
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31MasterySAQ-SDefinite integrals and the area under a curves6 marksPaper 2~9 min
A company manufactures decorative tiles. The curved edge of a tile is modelled by the function f(x)=82ln(x+1)f(x) = 8 - 2\ln(x+1), for 0x60 \leq x \leq 6, where xx is the horizontal distance from the left edge of the tile and f(x)f(x) is the vertical height above the base, both measured in centimetres.
(a)
Calculate the area of the tile, represented by the region enclosed by the curve y=f(x)y = f(x), the xx-axis, and the lines x=0x = 0 and x=6x = 6. Give your answer in the form a+blnca + b\ln c, where a,b,cZa, b, c \in \mathbb{Z}[4 marks]
(b)
The tile is cut along the vertical line x=kx = k, dividing it into two pieces of equal area. Calculate the value of kk, correct to 3 significant figures. [2 marks]
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32MasterySAQ-SIndefinite integrals and their propertiess8 marksPaper 2~12 min
The graph of f(x)=x32xf(x) = x^3 - 2x is shown for xRx \in \mathbb{R}. The shaded region is bounded by the curve, the xx-axis, and the vertical lines x=1x = -1 and x=2x = 2.
(a)
Find f(x)dx\displaystyle\int f(x)\,dx[2 marks]
(b)
Show that f(x)=x(x2)(x+2)f(x) = x(x - \sqrt{2})(x + \sqrt{2}), and hence state the xx-values in the interval [1,2][-1, 2] at which f(x)f(x) changes sign. [2 marks]
(c)
Calculate the total area of the shaded region. [4 marks]
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33MasterySAQ-SIndefinite integrals and their propertiess6 marksPaper 2~9 min
The graph shows f(x)f'(x), the derivative of f(x)f(x), for 0x60 \leq x \leq 6. The graph consists of three line segments joining the points (0,0)(0,0), (2,4)(2,4), (4,0)(4,0), and (6,2)(6,-2) in order. Given that f(0)=1f(0) = 1:
(a)
Find f(2)f(2)[2 marks]
(b)
Find f(6)f(6)[4 marks]
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34MasterySAQ-SIndefinite integrals and their propertiess6 marksPaper 2~9 min
The rate of change of the volume of water in a reservoir, measured in thousands of cubic metres per day, is modelled by R(t)=12t2120t+300R(t) = 12t^2 - 120t + 300 where tt is the time in days after 1 January 2020. The reservoir initially contained 50005000 thousand cubic metres of water.
(a)
Find an expression for V(t)V(t), the volume of water in the reservoir in thousands of cubic metres at time tt[3 marks]
(b)
Find the minimum volume of water in the reservoir during the first 1515 days, and state the day on which it occurs. [3 marks]
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35MasterySAQ-SIndefinite integrals and their propertiess6 marksPaper 2~9 min
The acceleration of a particle moving along a straight line is given by a(t)=6t4a(t) = 6t - 4, where t0t \geq 0 is time in seconds and a(t)a(t) is in ms2\text{m\,s}^{-2}. The initial velocity of the particle is v(0)=10ms1v(0) = 10\,\text{m\,s}^{-1} and the initial displacement is s(0)=0s(0) = 0.
(a)
Find an expression for the velocity v(t)v(t) of the particle at time tt[2 marks]
(b)
Find an expression for the displacement s(t)s(t) of the particle from its starting point at time tt[2 marks]
(c)
Determine the total distance travelled by the particle in the first 44 seconds. [2 marks]
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36MasterySAQ-SSolving first-order differential equationss6 marksPaper 2~9 min
A population of rabbits on an island is modelled by the differential equation dPdt=P(500P)1000\frac{dP}{dt} = \frac{P(500 - P)}{1000} where PP is the number of rabbits at time tt years, t0t \geq 0.
(a)
Show that the population is increasing when 0<P<5000 < P < 500[2 marks]
(b)
Given that P=100P = 100 when t=0t = 0, use the result 1P(500P)dP=1500lnP500P+C\int \frac{1}{P(500-P)}\,dP = \frac{1}{500}\ln\left|\frac{P}{500-P}\right| + C to show that P=5001+4et/2P = \dfrac{500}{1 + 4e^{-t/2}}[4 marks]
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37MasterySAQ-SSolving first-order differential equationss10 marksPaper 2~15 min
The rate of cooling of a cup of coffee is modelled by Newton's Law of Cooling: dTdt=k(TTs)\frac{dT}{dt} = -k(T - T_s) where TT is the temperature of the coffee in C^\circ\text{C} at time tt minutes, Ts=20CT_s = 20\,^\circ\text{C} is the constant room temperature, and k>0k > 0 is a constant.
(a)
Show that T=20+AektT = 20 + Ae^{-kt} satisfies the differential equation, where AA is a constant. [2 marks]
(b)
Initially the coffee is at 90C90\,^\circ\text{C}. After 5 minutes, the coffee has cooled to 60C60\,^\circ\text{C}. Calculate the value of kk, giving your answer correct to 3 significant figures. [4 marks]
(c)
Coffee is considered drinkable when its temperature is between 45C45\,^\circ\text{C} and 65C65\,^\circ\text{C}. Using your value of kk from part (b), determine the total length of time, in minutes, for which the coffee remains drinkable. Give your answer correct to 3 significant figures. [4 marks]
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38MasterySAQ-SSolving first-order differential equationss6 marksPaper 2~9 min
A population of bacteria grows at a rate proportional to its size. The population PP, measured in thousands, satisfies the differential equation dPdt=kP\frac{dP}{dt} = kP where tt is time in hours and kk is a positive constant. At t=0t = 0 the population is 10001000 bacteria. After 33 hours the population is 20002000 bacteria.
(a)
Solve the differential equation to show that P=ektP = e^{kt}[2 marks]
(b)
Determine the value of kk. Give your answer correct to 3 significant figures. [2 marks]
(c)
A second bacterial culture starts with 10001000 bacteria and grows according to P=emtP = e^{mt}, where m=2km = 2k. Determine how many hours earlier than the original culture this second culture reaches a population of 80008000 bacteria. Give your answer correct to 3 significant figures. [2 marks]
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39MasterySAQ-SSolving first-order differential equationss6 marksPaper 2~9 min
A tank contains 100100 litres of water with a dissolved pollutant concentration of 0.5kg0.5\,\text{kg} per litre. Fresh water enters the tank at a rate of 22 litres per minute, and the well-mixed solution leaves at the same rate. Let x(t)kgx(t)\,\text{kg} be the mass of pollutant in the tank at time tt minutes.
(a)
Show that dxdt=x50\dfrac{dx}{dt} = -\dfrac{x}{50}[2 marks]
(b)
Solve this differential equation, giving xx as a function of tt[2 marks]
(c)
Calculate the time taken for the pollutant mass to reduce to 10kg10\,\text{kg}. Give your answer correct to the nearest minute. [2 marks]
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40MasterySAQ-SSolving first-order differential equationss6 marksPaper 2~9 min
A population of bacteria in a laboratory culture grows according to the differential equation dPdt=kP\dfrac{dP}{dt} = kP, where PP is the population size at time tt days and kk is a positive constant. Initially, the population is 200 bacteria. After 3 days, the population has grown to 600 bacteria.
(a)
Solve the differential equation to show that P=200ektP = 200e^{kt}[3 marks]
(b)
Determine the value of kk, giving your answer correct to 3 significant figures. [2 marks]
(c)
The laboratory protocol requires the culture to be terminated once the population reaches 2000 bacteria. Calculate the time, in days, at which termination occurs. Give your answer correct to 3 significant figures. [1 mark]
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