Questions — Pre-U (885 questions)

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Pre-U Pre-U 9795/2 Specimen Q5
8 marks Moderate -0.3
A girl can paddle her canoe at \(5 \text{ m s}^{-1}\) in still water. She wishes to cross a river which is \(100 \text{ m}\) wide and flowing at \(8 \text{ m s}^{-1}\).
    1. Write down the angle to the river bank at which the boat must head, in order to cross the river in the least possible time. [1]
    2. Find the acute angle to the river bank at which the boat must head, in order to cross the river by the shortest route. [4]
  1. Calculate the times taken for each of the two cases in part (i). [3]
Pre-U Pre-U 9795/2 Specimen Q6
12 marks Challenging +1.8
A light elastic string of natural length \(2a\) and modulus of elasticity \(\lambda\) is stretched between two points \(A\) and \(B\), which are \(3a\) apart on a smooth horizontal table. A particle of mass \(m\) is attached to the mid-point of the string, pulled aside to \(A\) and released.
  1. Prove that, while one part of the string is taut and the other part is slack, the particle is describing simple harmonic motion. [2]
  2. Find the speed of the particle when the slack part of the string becomes taut. [2]
  3. Prove that the total time for the particle to reach the mid-point of the string for the first time is $$\sqrt{\frac{ma}{\lambda}} \left( \frac{\pi}{3} + \frac{1}{\sqrt{2}} \sin^{-1} \frac{1}{\sqrt{7}} \right).$$ [8]
Pre-U Pre-U 9795/2 Specimen Q7
6 marks Challenging +1.2
The length \(M\) of male snakes of a certain species may be regarded as a normal random variable with mean \(0.45\) metres and standard deviation \(0.06\) metres. The length \(F\) of female snakes of the same species may be regarded as a normal random variable with mean \(0.55\) metres and standard deviation \(0.08\) metres. Assuming that \(M\) and \(F\) are independent, find the probability that a randomly chosen male snake of this species is more than three-quarters of the length of a randomly chosen female snake of this species. [6]
Pre-U Pre-U 9795/2 Specimen Q8
9 marks Standard +0.3
  1. The random variable \(X\) is such that \(\text{E}(X) = a\theta + b\), where \(a\) and \(b\) are constants and \(\theta\) is a parameter. Show that \(\frac{X - b}{a}\) is an unbiased estimator of \(\theta\). [2]
  2. The continuous random variable \(X\) has probability density function given by $$f(x) = \begin{cases} \frac{1}{8}(\theta + 4 - x) & \theta \leq x \leq \theta + 4, \\ 0 & \text{otherwise}. \end{cases}$$ Find \(\text{E}(X)\) and hence find an unbiased estimator of \(\theta\). [7]
Pre-U Pre-U 9795/2 Specimen Q9
10 marks Standard +0.3
A certain type of fossil occurs at a mean rate of \(0.5\) per square metre at a particular location.
  1. State an assumption that must be made so that the above situation can be modelled by a Poisson distribution. [1]
  2. Find the probability of at least 7 of these fossils occurring in an area of \(10 \text{ m}^2\). [2]
  3. Given that at least 4 such fossils have occurred in an area of \(5 \text{ m}^2\), find the probability that there will be more than 6 found in this area of \(5 \text{ m}^2\). [3]
  4. Find the least area that must be searched in order that the probability of finding at least one fossil of this type is greater than \(0.999\). Give your answer to the nearest square metre. [4]
Pre-U Pre-U 9795/2 Specimen Q10
10 marks Standard +0.3
A biased tetrahedral die has faces numbered \(1\) to \(4\). The random variable \(X\) is the number on the face of the die which is in contact with the table after the die has been thrown. It is known, for this die, that \(\text{P}(X = x) = kx\) where \(k\) is a constant.
  1. Determine the value of \(k\) and state the moment generating function of \(X\). [3]
  2. Hence find \(\text{E}(X)\) and \(\text{Var}(X)\). [7]
Pre-U Pre-U 9795/2 Specimen Q11
12 marks Standard +0.3
  1. State briefly the conditions under which the binomial distribution \(\text{B}(n, p)\) may be approximated by a normal distribution. [2]
  2. A multiple-choice test has \(50\) questions. Each question has four possible answers. A student passes the test if answering \(36\%\) or more of the questions correctly. Using a suitable distributional approximation, estimate the probability that a student who selects answers to all the questions randomly will pass the test. [5]
  3. A test similar to that in part (ii) has \(N\) questions instead of \(50\) questions. Estimate the least value of \(N\) so that the probability that a student gets \(36\%\) or more of the questions correct, by selecting answers to all questions randomly, will be less than \(0.01\). (A continuity correction is not required in this part of the question.) [5]
Pre-U Pre-U 9795/2 Specimen Q12
13 marks Standard +0.8
The length of time, in years, that a salesman keeps his company car may be modelled by the continuous random variable \(T\). The probability density function of \(T\) is given by $$f(t) = \begin{cases} \frac{2}{5}t e^{-\frac{t^2}{5}} & t \geq 0, \\ 0 & \text{otherwise}. \end{cases}$$
  1. Sketch the graph of \(f(t)\). [2]
  2. Find the cumulative distribution function \(F(t)\) and hence find the median value of \(T\). [3]
  3. Find the probability that \(T\) is greater than the modal value of \(T\). [5]
  4. The probability that a randomly chosen salesman keeps his car longer than \(N\) years is \(0.05\). Find the value of \(N\) correct to \(3\) significant figures. [3]
Pre-U Pre-U 9794/2 Specimen Q1
4 marks Moderate -0.3
  1. Show that \(\binom{n}{n-2} = \frac{n(n-1)}{2}\), where the positive integer \(n\) satisfies \(n \geqslant 2\). [1]
  2. Solve the equation \(\binom{2n+1}{2n-1} - 2 \times \binom{n}{n-2} = 24\). [3]
Pre-U Pre-U 9794/2 Specimen Q2
4 marks Standard +0.3
Solve the simultaneous equations $$x - 2y = 5,$$ $$\frac{4}{x} - \frac{2}{y} = 5.$$ [4]
Pre-U Pre-U 9794/2 Specimen Q3
5 marks Standard +0.8
The equation of a curve is \(y = x^{\frac{3}{2}} \ln x\). Find the exact coordinates of the stationary point on the curve. [5]
Pre-U Pre-U 9794/2 Specimen Q4
7 marks Standard +0.3
A circle, of radius \(\sqrt{5}\) and centre the origin \(O\), is divided into two segments by the line \(y = 1\).
  1. Determine the area of the smaller segment. [4]
The line is rotated clockwise about \(O\) through \(45^{\circ}\) and then reflected in the \(x\)-axis.
  1. Find the equation of the line in its final position. [3]
Pre-U Pre-U 9794/2 Specimen Q5
9 marks Standard +0.3
  1. Divide the quartic \(2x^4 - 5x^3 + 4x^2 + 2x - 3\) by the quadratic \(x^2 + x - 2\), identifying the quotient and the remainder. [4]
    1. Show that \((x - 1)\) is a factor of \(nx^{n+1} - (n + 1)x^n + 1\), where \(n\) is a positive integer. [1]
    2. Hence, or otherwise, find all the roots of \(3x^4 - 4x^3 + 1 = 0\). [4]
Pre-U Pre-U 9794/2 Specimen Q6
10 marks Standard +0.8
  1. Express \(y^3 - 3y - 2\) in terms of \(x\), where \(x = y + 1\). [1]
  2. Hence express $$\frac{2y + 5}{y^3 - 3y - 2}$$ in partial fractions. [5]
  3. Find the exact value of $$\int_0^1 \frac{2y + 5}{y^3 - 3y - 2} dy.$$ [4]
Pre-U Pre-U 9794/2 Specimen Q7
12 marks Moderate -0.3
  1. Given that \(\cos \theta = \frac{7}{25}\), where \(\frac{3}{2}\pi < \theta < 2\pi\), determine the exact values of
    1. \(\sin \theta\), [3]
    2. \(\sin(\frac{1}{2}\theta)\), [3]
    3. \(\sec(\frac{1}{2}\theta)\). [1]
    1. Express \(4 \cos x - 3 \sin x\) in the form \(A \cos(x + \alpha)\), where \(A > 0\) and \(0 < \alpha < \frac{1}{2}\pi\). [2]
    2. Hence find the greatest and least values of \(4 \cos x - 3 \sin x\) for \(0 \leqslant x \leqslant \pi\). [3]
Pre-U Pre-U 9794/2 Specimen Q8
14 marks Standard +0.8
    1. Find the general solution of the differential equation $$x \frac{dy}{dx} = y(1 + x \cot x),$$ expressing \(y\) in terms of \(x\). [5]
    2. Find the particular solution given that \(y = 1\) when \(x = \frac{1}{2}\pi\). [2]
  1. The real variables \(x\) and \(y\) are related by \(x^2 - y^2 = 2ax - b\), where \(a\) and \(b\) are real constants.
    1. Show that \(\frac{dy}{dx} = 0\) can only be solved for \(x\) and \(y\) if \(b \geqslant a^2\). [5]
    2. Show that \(y \frac{d^2y}{dx^2} = 1 - \left(\frac{dy}{dx}\right)^2\). [2]
Pre-U Pre-U 9794/2 Specimen Q9
15 marks Challenging +1.3
Two curves are defined by \(y = x^k\) and \(y = x^{\frac{1}{k}}\), for \(x \geqslant 0\), where \(k > 0\).
  1. Prove that, except for one value of \(k\), the curves intersect in exactly two points. [4]
The two curves enclose a finite region \(R\).
  1. Find the area, \(A\), of \(R\), giving your answer in the form \(A = f(k)\) and distinguishing clearly between the cases \(k < 1\) and \(k > 1\). [4]
  2. Determine the set of values of \(k\) for which \(A \leqslant 0.5\). [3]
  3. The function \(f\) is given by \(f : x \mapsto A\) with \(k > 1\). Prove that \(f\) is one-one and determine its inverse. [4]
Pre-U Pre-U 9794/2 Specimen Q10
7 marks Moderate -0.3
  1. Determine the impulse of a force of magnitude \(6\) N that acts on a particle of mass \(3\) kg for \(1.5\) seconds. [1]
Particles \(A\) and \(B\), of masses \(0.1\) kg and \(0.2\) kg respectively, can move on a smooth horizontal table. Initially \(A\) is moving with speed \(3\) m s\(^{-1}\) towards \(B\), which is moving with speed \(1\) m s\(^{-1}\) in the same direction as the motion of \(A\). During a collision \(B\) experiences an impulse from \(A\) of magnitude \(0.2\) kg m s\(^{-1}\).
  1. Find the speeds of the particles immediately after the collision. [4]
  2. Determine the coefficient of restitution between the particles. [2]
Pre-U Pre-U 9794/2 Specimen Q11
11 marks Standard +0.3
A particle \(P\) of mass \(1.5\) kg is placed on a smooth horizontal table. The particle is initially at the origin of a \(2\)-dimensional vector system defined by perpendicular unit vectors \(\mathbf{i}\) and \(\mathbf{j}\) in the plane of the table. The particle is subject to three forces of magnitudes \(10\) N, \(12\) N and \(F\) N, acting in the directions of the vectors \(3\mathbf{i} + 4\mathbf{j}\), \(-\mathbf{j}\) and \(-\cos \theta \mathbf{i} + \sin \theta \mathbf{j}\) respectively, and no others.
  1. Given that the system is in equilibrium, determine \(F\) and \(\theta\). [6]
The force of magnitude \(12\) N is replaced by one of magnitude \(4\) N, but in the opposite direction. The particle is initially at rest.
  1. Find the position vector of the particle \(3\) seconds later. [5]
Pre-U Pre-U 9794/2 Specimen Q12
11 marks Standard +0.3
A particle \(P\) of mass \(2\) kg rests on a long rough horizontal table. The coefficient of friction between \(P\) and the table is \(0.2\). A light inextensible string has one end attached to \(P\) and the other end attached to a particle \(Q\) of mass \(4\) kg. The particle \(Q\) is placed on a smooth plane inclined at \(30^{\circ}\) to the horizontal. The string passes over a smooth light pulley fixed at a point in the line of intersection of the table and the plane (see diagram). \includegraphics{figure_12} Initially the system is held in equilibrium with the string taut. The system is released from rest at time \(t = 0\), where \(t\) is measured in seconds. In the subsequent motion \(P\) does not reach the pulley.
  1. Show that the magnitude of the acceleration of the particles is \(\frac{8}{3}\) m s\(^{-2}\). [4]
After the particles have moved a distance of \(12\) m the string is cut.
  1. Find the corresponding value of \(t\) and the speed of the particles at this instant. [4]
  2. Find the value of \(t\) when \(P\) comes to rest. [3]
Pre-U Pre-U 9794/2 Specimen Q13
11 marks Standard +0.3
A gunner fires one shell from each of two guns on a stationary ship towards a vertical cliff \(AB\) of height \(100\) m whose foot \(A\) is at a horizontal distance \(600\) m from the point of projection.
  1. Given that the shell from the first gun hits the cliff, travelling horizontally, at a point \(45\) m above \(A\), determine the initial velocity of the shell. Express your answer in the form \(a\mathbf{i} + b\mathbf{j}\), where \(a\) and \(b\) are integers. [6]
  2. The shell from the second gun hits the cliff at its top point \(B\). Given that the initial speed of the shell is \(300\) m s\(^{-1}\), determine the possible angles of projection. [5]
Pre-U Pre-U 9795 Specimen Q1
4 marks Standard +0.3
The region \(R\) of an Argand diagram is defined by the inequalities $$0 \leqslant \arg(z + 4\mathrm{i}) \leqslant \frac{1}{4}\pi \quad \text{and} \quad |z| \leqslant 4.$$ Draw a clearly labelled diagram to illustrate \(R\). [4]
Pre-U Pre-U 9795 Specimen Q2
6 marks Challenging +1.2
It is given that $$\mathrm{f}(n) = 7^n (6n + 1) - 1.$$ By considering \(\mathrm{f}(n + 1) - \mathrm{f}(n)\), prove by induction that \(\mathrm{f}(n)\) is divisible by 12 for all positive integers \(n\). [6]
Pre-U Pre-U 9795 Specimen Q3
6 marks Standard +0.3
Solve exactly the equation $$5 \cosh x - \sinh x = 7,$$ giving your answers in logarithmic form. [6]
Pre-U Pre-U 9795 Specimen Q4
6 marks Standard +0.3
Write down the sum $$\sum_{n=1}^{2N} n^3$$ in terms of \(N\), and hence find $$1^3 - 2^3 + 3^3 - 4^3 + \ldots - (2N)^3$$ in terms of \(N\), simplifying your answer. [6]