WAEC Further Mathematics 2017 past questions and answers

52 questions. Try each one, then open the answer to check yourself and read the explanation.

Question 1

Indices and Logarithms

If logy (1/8) = 3, find the value of y.

  1. A.−2
  2. B.−½
  3. C.½
  4. D.2
Show the answer and explanation

Answer: C (½)

Explanation

y³ = 1/8, so y = ½.

Open this question

Question 4

Polynomials

If x2 − kx + 9 = 0 has equal roots, find the values of k.

  1. A.3, 4
  2. B.±3
  3. C.±5
  4. D.±6
Show the answer and explanation

Answer: D (±6)

Explanation

Equal roots: k² − 36 = 0, so k = ±6.

Open this question

Question 5

Coordinate Geometry

Find the coordinates of the centre of the circle 3x2 + 3y2 − 4x + 8y − 2 = 0.

  1. A.(−2, 4)
  2. B.(−2/3, 4/3)
  3. C.(2/3, −4/3)
  4. D.(2, −4)
Show the answer and explanation

Answer: C ((2/3, −4/3))

Explanation

Divide by 3 first: x² + y² − (4/3)x + (8/3)y − 2/3 = 0. The centre is (2/3, −4/3).

Open this question

Question 6

Functions

The function f: x → √(4 − 2x) is defined on the set of real numbers R. Find the domain of f.

  1. A.x < 2
  2. B.x ≤ 2
  3. C.x = 2
  4. D.x > −2
Show the answer and explanation

Answer: B (x ≤ 2)

Explanation

We need 4 − 2x ≥ 0, i.e. x ≤ 2.

Open this question

Question 7

Functions

Given that f(x) = (x + 1)/2, find f−1(−2).

  1. A.−5
  2. B.−3
  3. C.3
  4. D.5
Show the answer and explanation

Answer: A (−5)

Explanation

f⁻¹(x) = 2x − 1, so f⁻¹(−2) = −5.

Open this question

Question 8

Polynomials

Given that (6x + m)/(2x2 + 7x − 15) = 4/(x + 5) − 2/(2x − 3), find the value of m.

  1. A.20
  2. B.12
  3. C.−10
  4. D.−22
Show the answer and explanation

Answer: D (−22)

Explanation

6x + m = 4(2x − 3) − 2(x + 5) = 6x − 22, so m = −22.

Open this question

Question 9

Binomial Theorem

Find the coefficent of x4 in the expansion of (1 − 2x)6.

  1. A.−320
  2. B.−240
  3. C.240
  4. D.320
Show the answer and explanation

Answer: C (240)

Explanation

⁶C₄(−2x)⁴ = 15 × 16x⁴ = 240x⁴.

Open this question

Question 10

Sequences and Series

Find the 21st term of the Arithmetic Progression (AP): −4, −1.5, 1, 3.5, …

  1. A.43.5
  2. B.46
  3. C.48.5
  4. D.51
Show the answer and explanation

Answer: B (46)

Explanation

a = −4, d = 2.5. T₂₁ = −4 + 20(2.5) = 46.

Open this question

Question 11

Permutations and Combinations

How many ways can six students be seated around a circular table?

  1. A.36
  2. B.48
  3. C.72
  4. D.120
Show the answer and explanation

Answer: D (120)

Explanation

Around a circle: (6 − 1)! = 120.

Open this question

Question 12

Matrices and Determinants

If (2 1 / 4 3)(5 / 4) = k(17.5 / 40.0), find the value of k. (Matrices written row by row; / separates the rows.)

  1. A.0.20
  2. B.0.40
  3. C.0.80
  4. D.1.25
Show the answer and explanation

Answer: C (0.80)

Explanation

The product is (14 / 32), and (14 / 32) = 0.8 × (17.5 / 40), so k = 0.80.

Open this question

Question 13

Trigonometry

Express Cos 150° in surd form.

  1. A.−√3
  2. B.−√3/2
  3. C.−½
  4. D.√2/2
Show the answer and explanation

Answer: B (−√3/2)

Explanation

cos 150° = −cos 30° = −√3/2.

Open this question

Question 14

Coordinate Geometry

A straight line parallel to 2x + 3y = 6, passes through the point (−1, 2). Find the equation of the line.

  1. A.2x − 3y = 2
  2. B.2x + 3y = −2
  3. C.2x + 3y = −4
  4. D.2x + 3y = 4
Show the answer and explanation

Answer: D (2x + 3y = 4)

Explanation

A parallel line is 2x + 3y = c; through (−1, 2): c = −2 + 6 = 4.

Open this question

Question 15

Polynomials

α and β are the roots of the equation 2x2 − 3x + 4 = 0. Find (α + β).

  1. A.−2
  2. B.−3/2
  3. C.3/2
  4. D.2
Show the answer and explanation

Answer: C (3/2)

Explanation

α + β = −b/a = 3/2.

Open this question

Question 16

Polynomials

α and β are the roots of the equation 2x2 − 3x + 4 = 0. Find (α/β + β/α).

  1. A.−9/8
  2. B.−7/8
  3. C.7/8
  4. D.9/8
Show the answer and explanation

Answer: B (−7/8)

Explanation

αβ = 2. α/β + β/α = ((α + β)² − 2αβ)/αβ = (9/4 − 4)/2 = −7/8.

Open this question

Question 17

Matrices and Determinants

If B = (2 5 / 1 3), find B−1. (Matrices written row by row; / separates the rows.)

  1. A.(−3 −5 / 1 2)
  2. B.(3 −5 / 1 2)
  3. C.(3 −5 / −1 2)
  4. D.(−3 5 / 1 −2)
Show the answer and explanation

Answer: C ((3 −5 / −1 2))

Explanation

|B| = 6 − 5 = 1. B⁻¹ = (3 −5 / −1 2): swap the diagonal and change the signs of both off-diagonal entries.

Open this question

Question 18

Trigonometry

Given that sin x = 5/13 and sin y = 8/17, where x and y are acute, find the value of cos (x + y).

  1. A.130/221
  2. B.140/221
  3. C.140/204
  4. D.220/23
Show the answer and explanation

Answer: B (140/221)

Explanation

cos x = 12/13, cos y = 15/17. cos(x + y) = 180/221 − 40/221 = 140/221.

Open this question

Question 20

Differentiation

Given that f(x) = 5x2 − 4x + 3, find the coordinates of the point where the gradient is 6.

  1. A.(4, 1)
  2. B.(4, −2)
  3. C.(1, 4)
  4. D.(1, −2)
Show the answer and explanation

Answer: C ((1, 4))

Explanation

f′(x) = 10x − 4 = 6 gives x = 1, and f(1) = 5 − 4 + 3 = 4. The point is (1, 4).

Open this question

Question 21

Differentiation

If y = (1 + x)/(1 − x), find dy/dx.

  1. A.2/(1 − x)2
  2. B.−2/(1 − x)2
  3. C.−1/√(1 − x)
  4. D.1/√(1 − x)
Show the answer and explanation

Answer: A (2/(1 − x)2)

Explanation

Quotient rule: [(1 − x) + (1 + x)]/(1 − x)² = 2/(1 − x)².

Open this question

Question 22

Integration

Evaluate ∫−10 (x + 1)(x − 2) dx

  1. A.7/6
  2. B.5/6
  3. C.−5/6
  4. D.−7/6
Show the answer and explanation

Answer: D (−7/6)

Explanation

∫(x² − x − 2) dx = x³/3 − x²/2 − 2x. From −1 to 0: 0 − (−1/3 − 1/2 + 2) = −7/6.

Open this question

Question 23

Surds

Simplify: √128/(√32 − 2√2).

  1. A.4√2
  2. B.3√2
  3. C.3
  4. D.4
Show the answer and explanation

Answer: D (4)

Explanation

√128 = 8√2 and √32 = 4√2, so 8√2/(2√2) = 4.

Open this question

Question 24

Permutations and Combinations

There are 7 boys in a class of 20. Find the number of ways of selecting 3 girls and 2 boys.

  1. A.1638
  2. B.2730
  3. C.6006
  4. D.7520
Show the answer and explanation

Answer: C (6006)

Explanation

13 girls: ¹³C₃ × ⁷C₂ = 286 × 21 = 6006.

Open this question

Question 25

Sequences and Series

The 3rd and 7th terms of a Geometric Progression (G.P) are 81 and 16 respectively. Find the 5th term.

  1. A.4/729
  2. B.16/81
  3. C.27
  4. D.36
Show the answer and explanation

Answer: D (36)

Explanation

r⁴ = 16/81, so r² = 4/9. T₅ = T₃ × r² = 81 × 4/9 = 36.

Open this question

Question 26

Differentiation

Differentiate (5x3 + x2)/x, x ≠ 0 with respect to x

  1. A.10x + 1
  2. B.10x + 2
  3. C.x(15x + 1)
  4. D.x(15x + 2)
Show the answer and explanation

Answer: A (10x + 1)

Explanation

Simplify first: 5x² + x, whose derivative is 10x + 1.

Open this question

Question 27

Polynomials

A curve is given by y = 5 − x − 2x2. Find the equation of its line of symmetry.

  1. A.x = −41/8
  2. B.x = −1/4
  3. C.x = 1/4
  4. D.x = 41/8
Show the answer and explanation

Answer: B (x = −1/4)

Explanation

The axis of symmetry passes through the turning point: dy/dx = −1 − 4x = 0, so x = −1/4.

Open this question

Question 28

Statistics

In a class of 10 boys and 15 girls, the average score in a Biology test is 90. If the average score for the girls is x, find the average score for the boys in terms of x.

  1. A.200 − (2/3)x
  2. B.225 − (3/2)x
  3. C.250 − 2x
  4. D.250 − 3x
Show the answer and explanation

Answer: B (225 − (3/2)x)

Explanation

Total = 25 × 90 = 2250. Boys' total = 2250 − 15x, so their average is 225 − (3/2)x.

Open this question

Question 29

Probability

A fair die is tossed twice. What is the sample size?

  1. A.6
  2. B.12
  3. C.36
  4. D.48
Show the answer and explanation

Answer: C (36)

Explanation

6 × 6 = 36 outcomes.

Open this question

Question 30

Vectors

Given that a = (2, 3) and b = (−1, 4) (column vectors), evaluate (2a − ¼b).

  1. A.(17/4, 7)
  2. B.(17/4, 5)
  3. C.(17/4, 3)
  4. D.(17/4, 2)
Show the answer and explanation

Answer: B ((17/4, 5))

Explanation

2a = (4, 6) and ¼b = (−¼, 1). 2a − ¼b = (4¼, 5) = (17/4, 5).

Open this question

Question 31

Probability

The table shows the results of tossing a fair die 150 times.
Face: 1, 2, 3, 4, 5, 6
Frequency: 12, 18, y, 30, 2y, 45
Find the probability of obtaining a 5.

  1. A.1/10
  2. B.1/6
  3. C.1/5
  4. D.3/10
Show the answer and explanation

Answer: C (1/5)

Explanation

105 + 3y = 150 gives y = 15, so a 5 came up 2y = 30 times. P = 30/150 = 1/5.

Open this question

Question 32

Statistics

The table shows the results of tossing a fair die 150 times.
Face: 1, 2, 3, 4, 5, 6
Frequency: 12, 18, y, 30, 2y, 45
Find the mode.

  1. A.3
  2. B.4
  3. C.5
  4. D.6
Show the answer and explanation

Answer: D (6)

Explanation

With y = 15 the frequencies are 12, 18, 15, 30, 30, 45. Face 6 occurs most often, so the mode is 6.

Open this question

Question 33

Vectors

Given that a = 5i + 4j and b = 3i + 7j, evaluate (3a − 8b).

  1. A.9i + 44j
  2. B.−9i + 44j
  3. C.−9i − 44j
  4. D.9i − 44j
Show the answer and explanation

Answer: C (−9i − 44j)

Explanation

3a − 8b = (15 − 24)i + (12 − 56)j = −9i − 44j.

Open this question

Question 34

Dynamics

A force (10i + 4j)N acts on a body of mass 2 kg which is at rest. Find the velocity after 3 seconds.

  1. A.(5/3 i + 2/3 j) ms−1
  2. B.(10/3 i + 4/3 j) ms−1
  3. C.(5i + 2j) ms−1
  4. D.(15i + 6j) ms−1
Show the answer and explanation

Answer: D ((15i + 6j) ms−1)

Explanation

a = F/m = 5i + 2j; v = at = 3(5i + 2j) = 15i + 6j ms⁻¹.

Open this question

Question 35

Vectors

Find the magnitude and direction of the vector p = (5i − 12j).

  1. A.(13, 113.38°)
  2. B.(13, 067.38°)
  3. C.(13, 025.38°)
  4. D.(13, 157.38°)
Show the answer and explanation

Answer: D ((13, 157.38°))

Explanation

|p| = √(25 + 144) = 13. p points 5 east and 12 south, so its bearing is 90° + tan⁻¹(12/5) = 90° + 67.38° = 157.38°.

Open this question

Question 36

Indices and Logarithms

Solve: 32x − 3x+2 = 3x+1 − 27.

  1. A.1 or 0
  2. B.1 or 2
  3. C.1 or −2
  4. D.−1 or 2
Show the answer and explanation

Answer: B (1 or 2)

Explanation

Let p = 3ˣ: p² − 9p = 3p − 27, so p² − 12p + 27 = 0, p = 3 or 9. x = 1 or 2.

Open this question

Question 37

Dynamics

The velocity, V, of a particle, in ms−1, after t seconds, is V = 3t2 + 2t − 1. Find the acceleration of the particle after 2 seconds.

  1. A.10 ms−2
  2. B.13 ms−2
  3. C.14 ms−2
  4. D.17 ms−2
Show the answer and explanation

Answer: C (14 ms−2)

Explanation

a = dV/dt = 6t + 2 = 14 ms⁻² at t = 2.

Open this question

Question 38

Functions

Given that f(x) = 2x2 − 3 and g(x) = x + 1, where x ∈ R, find g o f(x).

  1. A.2(x2 − 1)
  2. B.2x2 + 4x − 1
  3. C.2x2 + 6x − 1
  4. D.3(x2 − 1)
Show the answer and explanation

Answer: A (2(x2 − 1))

Explanation

g(f(x)) = (2x² − 3) + 1 = 2x² − 2 = 2(x² − 1).

Open this question

Question 39

Polynomials

If (2x2 − x − 3) is a factor of f(x) = 2x3 − 5x2 − x + 6, find the other factor.

  1. A.(x − 2)
  2. B.(x − 1)
  3. C.(x + 1)
  4. D.(x + 3/2)
Show the answer and explanation

Answer: A ((x − 2))

Explanation

(2x² − x − 3)(x − 2) = 2x³ − 5x² − x + 6, so the other factor is (x − 2).

Open this question

Question 40

Sets and Logic

If P = {n2 + 1 : n = 0, 2, 3} and Q = {n + 1 : n = 2, 3, 5}, find P ∩ Q.

  1. A.{5, 10}
  2. B.{4, 6}
  3. C.{1, 3}
  4. D.{ }
Show the answer and explanation

Answer: D ({ })

Explanation

P = {1, 5, 10} and Q = {3, 4, 6}. They have no common member, so P ∩ Q = { }.

Open this question

Theory question 101

Functions

(a) If f(x) = (4 − 5x)/2 and g(x) = x + 6, x ∈ R, find f o g−1
(b) P(x, y) divides the line joining (7, −5) and (−2, 7) internally in the ratio 5:4. Find the coordinates of P.

Show the model answer
Model answer

(a) g⁻¹(x) = x − 6. f(g⁻¹(x)) = (4 − 5(x − 6))/2 = (34 − 5x)/2.
(b) x = (5(−2) + 4(7))/9 = 2; y = (5(7) + 4(−5))/9 = 5/3. P(2, 5/3).

Explanation

For internal division in m : n use (mx₂ + nx₁)/(m + n).

Open this question

Theory question 102

Integration

Evaluate ∫13 (x − 1)/(x + 1)2 dx.

Show the model answer
Model answer

(x − 1)/(x + 1)² = 1/(x + 1) − 2/(x + 1)².
∫ = [ln(x + 1) + 2/(x + 1)] from 1 to 3 = (ln 4 + ½) − (ln 2 + 1) = ln 2 − ½ ≈ 0.193.

Explanation

Split the fraction first (write x − 1 as (x + 1) − 2).

Open this question

Theory question 103

Indices and Logarithms

(a) Given that log10 p = a, log10 q = b and log10 s = c, express log10(p1/3q4/s2) in terms of a, b and c.
(b) The radius of a circle is 6 cm. If the area of the circle is increasing at the rate of 20 cm2s−1, find, leaving the answer in terms of π, the rate at which the radius is increasing.

Show the model answer
Model answer

(a) ⅓log p + 4 log q − 2 log s = a/3 + 4b − 2c.
(b) A = πr², dA/dt = 2πr dr/dt. 20 = 12π dr/dt, so dr/dt = 5/(3π) cm s⁻¹.

Explanation

Connect the rates with the chain rule.

Open this question

Theory question 104

Polynomials

If (x + 1) and (x − 2) are factors of the polynomial g(x) = x4 + ax3 + bx2 − 16x − 12, find the values of a and b.

Show the model answer
Model answer

g(−1) = 1 − a + b + 16 − 12 = 0, so b − a = −5.
g(2) = 16 + 8a + 4b − 32 − 12 = 0, so 2a + b = 7.
Subtracting: 3a = 12, a = 4, b = −1.

Explanation

Use the factor theorem twice.

Open this question

Theory question 105

Probability

Bottles of the same sizes produced in a factory are packed in boxes. Each box contains 10 bottles. If 8% of the bottles produced are defective, find correct to two decimal places, the probability that a box chosen at random contains at least three defective bottles.

Show the model answer
Model answer

Binomial: n = 10, p = 0.08, q = 0.92.
P(0) = 0.4344, P(1) = 0.3777, P(2) = 0.1478.
P(X ≥ 3) = 1 − 0.9599 ≈ 0.04.

Explanation

'At least three' = 1 − P(0, 1 or 2).

Open this question

Theory question 106

Statistics

The table shows the heights in cm of some seedlings in a certain garden:
Height (cm): 36 − 40, 41 − 45, 46 − 50, 51 − 55, 56 − 60
Frequency: 3, 9, 21, 12, 5
(a) Draw a cumulative frequency curve for the distribution (b) Using the curve in 6(a), find the semi-interquartile range.

Show the model answer
Model answer

(a) Upper boundaries 40.5, 45.5, 50.5, 55.5, 60.5; cumulative frequencies 3, 12, 33, 45, 50. Plot (start at (35.5, 0)) and join with a smooth curve.
(b) Q₁ (12.5th) ≈ 45.6 cm; Q₃ (37.5th) ≈ 52.4 cm.
Semi-interquartile range = ½(52.4 − 45.6) ≈ 3.4 cm (values read from a graph may differ slightly).

Explanation

Read the quartiles at a quarter and three quarters of the total frequency.

Open this question

Theory question 107

Coordinate Geometry

A parallelogram MNQR has vertices M(4, −6), N(10, 2), Q(8, 16) and R(x, y). Find the coordinates of R.

Show the model answer
Model answer

Diagonals MQ and NR bisect each other: M + Q = N + R.
R = (4 + 8 − 10, −6 + 16 − 2) = (2, 8).

Explanation

The diagonals of a parallelogram share a midpoint.

Open this question

Theory question 108

Statics

Forces F1 (18 N, 330°), F2 (10 N, 090°) and F3 (25 N, 180°) act on a body at rest. Find, correct to one decimal place, the magnitude and direction of the resultant force.

Show the model answer
Model answer

Components (east, north) = (F sin θ, F cos θ):
F₁ = (−9, 15.59); F₂ = (10, 0); F₃ = (0, −25).
Resultant = (1, −9.41); magnitude ≈ 9.5 N.
Direction: bearing 180° − tan⁻¹(1/9.41) ≈ 173.9°.

Explanation

Resolve each force into east and north components.

Open this question

Theory question 109

Trigonometry

(a) Simplify: 1/(1 − cos θ) + 1/(1 + cos θ) and leave the answer in terms of sin θ.
(b) Find the equation of the line joining the stationary points of y = x2(x − 3) and the distance between them.

Show the model answer
Model answer

(a) (1 + cos θ + 1 − cos θ)/(1 − cos²θ) = 2/sin²θ.
(b) y = x³ − 3x²; dy/dx = 3x² − 6x = 0 at x = 0 and 2. Points (0, 0) and (2, −4).
Line: y = −2x. Distance = √(4 + 16) = 2√5 ≈ 4.47.

Explanation

1 − cos²θ = sin²θ.

Open this question

Theory question 110

Polynomials

(a) If f(x) = (2x − 3)/((x2 − 1)(x − 2)), (i) find the values of x for which f(x) is undefined. (ii) express f(x) in partial fractions.
(b) A circle with centre (−3, 1) passes through the point (3, 1). Find its equation.

Show the model answer
Model answer

(a)(i) x = 1, −1 or 2.
(ii) A/(x − 1) + B/(x + 1) + C/(x − 2): x = 1 gives A = ½; x = −1 gives B = −5/6; x = 2 gives C = ⅓.
f(x) = 1/(2(x − 1)) − 5/(6(x + 1)) + 1/(3(x − 2)).
(b) r = 6: (x + 3)² + (y − 1)² = 36, i.e. x² + y² + 6x − 2y − 26 = 0.

Explanation

Factorise x² − 1 first.

Open this question

Theory question 111

Integration

(a) If f(x) = ∫(4x − x2) dx and f(3) = 21, find f(x).
(b) The second, fourth and eight terms of an Arithmetic Progression (A.P.) form the first three consecutive terms of a Geometric Progression (G.P.). The sum of the third and fifth terms of the A.P. is 20. Find the: (i) first four terms of the A.P., (ii) sum of the first ten terms of the A.P.

Show the model answer
Model answer

(a) f(x) = 2x² − x³/3 + c; f(3) = 18 − 9 + c = 21, c = 12. f(x) = 2x² − x³/3 + 12.
(b) (a + 3d)² = (a + d)(a + 7d) gives 2d² = 2ad, so a = d.
(a + 2d) + (a + 4d) = 8d = 20, d = 2.5 = a.
(i) 2.5, 5, 7.5, 10.
(ii) S₁₀ = 5(5 + 22.5) = 137.5.

Explanation

For G.P. terms, (middle)² = first × third.

Open this question

Theory question 112

Probability

(a) In a school, the ratio of those who passed to those who failed in a History test is 4 : 1. If 7 students are selected at random from the school, find, correct to two decimal places, the probability that: (i) at least 3 students passed the test: (ii) between 3 and 6 students failed the test. (b) A fair die is thrown five times, find the probability of obtaining a six three times.

Show the model answer
Model answer

P(pass) = 0.8, P(fail) = 0.2, n = 7.
(a)(i) 1 − P(0, 1 or 2 pass) = 1 − 0.0047 ≈ 1.00 (0.9953).
(ii) Between 3 and 6 (4 or 5 failed): ⁷C₄(0.2)⁴(0.8)³ + ⁷C₅(0.2)⁵(0.8)² ≈ 0.0287 + 0.0043 = 0.03. (Including 3 and 6: ≈ 0.15.)
(b) ⁵C₃(1/6)³(5/6)² = 250/7776 = 125/3888 ≈ 0.032.

Explanation

Use the binomial distribution with the right probability for each event.

Open this question

Theory question 113

Statistics

The table shows the frequency distribution of the ages of patients in a clinic.
Age (years): 17 − 19, 20 − 22, 23 − 28, 29 − 34, 35 − 43
No of patients: 6, 9, 12, 18, 18
(a) Draw a histogram for the distribution. (b) Find, correct to two decimal places, the mean age of the patients.

Show the model answer
Model answer

(a) Boundaries 16.5, 19.5, 22.5, 28.5, 34.5, 43.5 (widths 3, 3, 6, 6, 9). Plot frequency density (per 3 years): 6, 9, 6, 9, 6, as touching bars.
(b) Class marks 18, 21, 25.5, 31.5, 39; Σf = 63; Σfx = 108 + 189 + 306 + 567 + 702 = 1872.
Mean = 1872/63 ≈ 29.71 years.

Explanation

With unequal class widths, plot frequency densities.

Open this question

Theory question 114

Statics

(a) A body P of mass q kg is suspended by two light inextensible strings AB and DB attached to a horizontal table. The strings are inclined at 30° and 60° respectively to the horizontal and the tension in AB is 48 N. If the system is in equilibrium: (i) sketch a diagram to represent the information; (ii) calculate the tension in DB, (iii) find the value of q. [Take g = 10 ms−2]
(b) A ball is thrown vertically upwards with a velocity of 20 ms−1. Find, correct to two decimal places the: (i) maximum height reached by the ball; (ii) time taken to reach the maximum height. [Take g = 10 ms−2]

Show the model answer
Model answer

(a)(i) Sketch: B below the support line, BA at 30° and BD at 60° to the horizontal on opposite sides, weight 10q N straight down.
(ii) Horizontally: 48 cos 30° = T cos 60°, so T = 83.14 N.
(iii) Vertically: 48 sin 30° + 83.14 sin 60° = 24 + 72 = 96 = 10q, so q = 9.6.
(b)(i) v² = u² − 2gh: h = 400/20 = 20.00 m.
(ii) t = u/g = 2.00 s.

Explanation

Resolve the tensions horizontally and vertically.

Open this question

Theory question 115

Vectors

(a) Given that m = (6i + 8j) and n = (−8i + (7/3)j), find the: (i) magnitudes and directions of m and n, (ii) angle between m and n.
(b) The position vectors of points P, Q, R, S are (−2, 3), (10, 4), (3, 12) and (4, 0) (column vectors) respectively. Show that PQ is pependicular to RS

Show the model answer
Model answer

(a)(i) |m| = 10, at tan⁻¹(8/6) = 53.13° to the positive x-axis (bearing 036.87°).
|n| = √(64 + 49/9) = 25/3 ≈ 8.33, at 180° − tan⁻¹(7/24) = 163.74° to the positive x-axis (bearing 286.26°).
(ii) m·n = −48 + 56/3 = −88/3; cos θ = (−88/3)/(10 × 25/3) = −0.352, θ ≈ 110.61°.
(b) PQ = (12, 1), RS = (1, −12); PQ·RS = 12 − 12 = 0, so PQ ⊥ RS.

Explanation

Two vectors are perpendicular when their dot product is zero.

Open this question