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A particle is undergoing simple harmonic motion with period \( \frac{\pi}{3} \) - HSC - SSCE Mathematics Extension 2 - Question 13 - 2020 - Paper 1

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A particle is undergoing simple harmonic motion with period \( \frac{\pi}{3} \). The central point of motion of the particle is at \( x = -\sqrt{3} \). When \( t = 0... show full transcript

Worked Solution & Example Answer:A particle is undergoing simple harmonic motion with period \( \frac{\pi}{3} \) - HSC - SSCE Mathematics Extension 2 - Question 13 - 2020 - Paper 1

Step 1

Find an equation for the displacement, x, of the particle in terms of t.

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Answer

The equation has the form:

x(t)=Acos(nt)+Cx(t) = A \cos(nt) + C

Where:

  • (A = \frac{2}{\sqrt{3}})
  • (C = -\sqrt{3})
  • The angular frequency (n) is given by (n = \frac{2\pi}{T} = \frac{2\pi}{\frac{\pi}{3}} = 6)

Thus, substituting these values into the equation:

x(t)=23cos(6t)3x(t) = \frac{2}{\sqrt{3}} \cos(6t) - \sqrt{3}

Step 2

Consider the two lines in three dimensions given by ...

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Answer

To find the point of intersection, equate the components of the two lines:

  1. For x-component:
    (3 + 2h_1 = -6 + 3h_2 \Rightarrow (1))

  2. For y-component:
    (-1 + h_1 = 2 + 2h_2 \Rightarrow (2))

  3. For z-component:
    (7 + h_1 = -2 - 3h_2 \Rightarrow (3))

From equation (1):
(2h_2 - 2h_1 = 9 \Rightarrow h_2 = 1 + h_1)

Substituting (h_2) into (2):
(-1 + h_1 = 2 + 2(1 + h_1) \Rightarrow -1 + h_1 = 4 + 2h_1)

Solving gives:
( -1 - 4 = 2h_1 - h_1 \Rightarrow h_1 = -5 ) and substituting back into equation gives (h_2 = -4.

Finally, substituting (h_1) and (h_2) back into the line equation gives the point of intersection as:

r=(2 32 5)\mathbf{r} = \begin{pmatrix} -2 \ \frac{3}{2} \ -5 \end{pmatrix}

Step 3

By considering the right-angled triangle below, or otherwise, prove that a + b \over 2 \geq \sqrt{ab}.

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Answer

By Pythagoras, we have:

(a+b)2=x2+(ab)2x2=(a+b)2(ab)2 (a + b)^2 = x^2 + (a - b)^2 \Rightarrow x^2 = (a + b)^2 - (a - b)^2

The properties of the triangle imply: (x \leq a + b) Thus, it can be shown that: ( \frac{a + b}{2} \geq \sqrt{ab} ) using the inequality of means (AM-GM).

Step 4

Prove that p^2 + 4q^2 \geq 4pq.

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Answer

Let (p = a) and (q = b), then:

By following the derivation steps, we arrive at:

p2+4q24pq=(p2q)20,p^2 + 4q^2 - 4pq = (p - 2q)^2 \geq 0, which confirms that the inequality holds.

Step 5

Show that for any integer n, e^{iθ} + e^{-iθ} = 2cos(nθ).

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Answer

Using Euler's formula, we have:

eiθ=cos(θ)+isin(θ) and eiθ=cos(θ)isin(θ).e^{i\theta} = \cos(\theta) + i\sin(\theta) \text{ and } e^{-i\theta} = \cos(\theta) - i\sin(\theta).

Thus,

eiθ+eiθ=2cos(θ).e^{i\theta} + e^{-i\theta} = 2\cos(\theta).

Step 6

By expanding (e^{iθ} + e^{-iθ})^2, show that cos^2(θ) = 1/8 (cos(4θ) + 4cos(2θ) + 3).

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Answer

Starting with:

(eiθ+eiθ)2=2cos(θ)2cos(θ)=4cos2(θ),(e^{i\theta} + e^{-i\theta})^2 = 2\cos(\theta)\cdot 2\cos(\theta) = 4\cos^2(\theta),

and using the cosine of double angle:

cos(2θ)=2cos2(θ)1\cos(2\theta) = 2\cos^2(\theta) - 1

we derive the required expression through expansions.

Step 7

Consequently, or otherwise, find \int_{0}^{\frac{\pi}{2}} \cos^2(θ) \, dθ.

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Answer

Using the identity derived:

0π2cos2(θ)dθ=0π218(cos(4θ)+4cos(2θ)+3)dθ\int_{0}^{\frac{\pi}{2}} \cos^2(\theta) \, d\theta = \int_{0}^{\frac{\pi}{2}} \frac{1}{8}(\cos(4\theta) + 4\cos(2\theta) + 3) \, d\theta

Calculating each integral gives:

=[3π16]0+3π16= \left[ \frac{3\pi}{16} \right] - 0 + \frac{3\pi}{16}.

Finally, the answer results in ( \frac{3\pi}{16} ).

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