Answer:
(a) His speed when he runs from C to A is [tex]4.\overline {285714}[/tex] m/s
(i) The bearing of B from A is approximately 127.18°
(ii) The bearing of A from B is approximately 307.18°
Step-by-step explanation:
(a) The given parameters are;
The distance from A to B = 120 m
The speed with which Olay runs from A to B, v₁ = 4 m/s
The distance from B to C = 180 m
The speed with which Olay runs from B to C, v₂ = 3 m/s
The distance from C to A = 150 m
His average speed for the whole journey = 3.6 m/s
We find
The total distance of running from A back to A, d = 120 m + 180 m + 150 m = 450 m
The time it takes to run from A to B, t₁ = 120 m/(4m/s) = 30 seconds
The time it takes to run from B to C, t₂ = 180 m/(3m/s) = 60 seconds
Let t₃ represent the time it takes Olay to run from C to A
We have;
The total time it takes to run from A back to A = t₁ + t₂ + t₃
Therefore;
[tex]Average \ velocity = \dfrac{Total \ distance }{Total \ time} = \dfrac{d}{t_1 + t_2 + t_3}[/tex]
Substituting the known values for the average velocity, 'd', 't₁' and 't₂' gives;
[tex]Average \ velocity = 3.6 \, m/s = \dfrac{450 \, m}{30 \, s + 60 \, s + t_3}[/tex]
3.6 m/s × (30 s + 60 s + t₃) = 450 m
3.6 m/s × 30 s + 3.6 m/s × 60 s + 3.6 m/s × t₃ = 450 m
108 m + 216 m + 3.6 m/s × t₃ = 450 m
∴ 3.6 m/s × t₃ = 450 m - (108 m + 216 m) = 126 m
t₃ = 126 m/(3.6 m/s) = 35 s
The speed with which Olay runs from C to A, v₃ = Distance from C to A/t₃
The speed with which he runs from C to A = 150 m/(35 s) = 30/7 m/s =[tex]4.\overline {285714}[/tex] m/s
(i) The given bearing of C from A = 210°
By cosine rule, we have;
a² = b² + c² - 2·b·c·cos(A)
∴ cos(A) = (b² + c² - a²)/(2·b·c)
Where;
a = The distance from B to C = 180 m
b = The distance from C to A = 150 m
c = The distance from A to B = 120 m
We find;
cos(A) = (150² + 120² - 180²)/(2 × 150 × 120) = 0.125
A = arccos(0.125) ≈ 82.82°
The bearing of B from A ≈ 210° - 82.82° ≈ 127.18°
The bearing of B from A ≈ 127.18°
(ii) The angle, θ, formed by the path of the bearing of A from B is an alternate to the supplementary angle of the bearing of B from A
Therefore, we have;
θ ≈ 180°- 127.18° ≈ 52.82°
The bearing of A from B = The sum of angle at a point less θ
∴ The bearing of A from B = 360° - 52.82° ≈ 307.18°
The bearing of A from B ≈ 307.18°.
