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Complete the table below by filling in the missing lengths - Leaving Cert Mathematics - Question 7 - 2021

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Complete the table below by filling in the missing lengths. Swing 1 2 3 4 5 Length of Arc (cm) 45 81 729 20 200 $T_n = 45(0.9)^{n-1}$ Fi... show full transcript

Worked Solution & Example Answer:Complete the table below by filling in the missing lengths - Leaving Cert Mathematics - Question 7 - 2021

Step 1

Complete the table below by filling in the missing lengths.

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Answer

The lengths of the arc can be calculated from the formula: Ln=45(0.9)n1L_n = 45(0.9)^{n-1}

SwingLength of Arc (cm)
145
245(0.9)^{1} = 40.5
345(0.9)^{2} = 36.45
445(0.9)^{3} = 32.805
545(0.9)^{4} = 29.5245

Step 2

Find the arc length of swing 25.

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Answer

Using the formula for the arc length: T25=45(0.9)24T_{25} = 45(0.9)^{24} Calculating: T253.6extcmT_{25} ≈ 3.6 ext{ cm}

Step 3

Find the total distance travelled by the tip of the pendulum when it has completed swing 40.

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Answer

The distance can be found by summing up the lengths for the first 40 swings: S40=45+40.5+36.45+...+(45(0.9)39)S_{40} = 45 + 40.5 + 36.45 + ... + \left( 45(0.9)^{39} \right) Using the series sum formula: Sn=a(1rn)1rS_n = \frac{a(1-r^n)}{1-r} where a=45a = 45 and r=0.9r = 0.9, we find: S40443extcmS_{40} ≈ 443 ext{ cm}

Step 4

Swing p is the first swing which has an arc length of less than 2 cm. Find the value of p.

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Answer

Set the equation 45(0.9)p1<245(0.9)^{p-1} < 2. Solving for pp gives: p=log0.9(245)+1p = \lceil \log_{0.9}(\frac{2}{45}) + 1 \rceil Calculating gives approximately: p31p ≈ 31

Step 5

If the length of the pendulum is 1 m, show that the angle, θ, of swing 1 of the pendulum is 26°, correct to the nearest degree.

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Answer

Using the formula for the arc length: L=rθL = r \theta Here, r=100r = 100 cm and L=45L = 45 cm: 45=100θθ=45100=0.45extradians45 = 100\theta \Rightarrow \theta = \frac{45}{100} = 0.45 ext{ radians} Converting to degrees: θ=0.45×180π26°\theta = 0.45 \times \frac{180}{\pi} \approx 26°

Step 6

Hence, find the total accumulated angle that the pendulum swings through.

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Answer

The total angle for swings 1 to 40 is: =26+26(0.9)+26(0.92)+...+26(0.939)\sum = 26 + 26(0.9) + 26(0.9^2) + ... + 26(0.9^{39}) This series sums to: Total=26×1(0.9)4010.9260°\text{Total} = 26 \times \frac{1 - (0.9)^{40}}{1 - 0.9} ≈ 260°

Step 7

Hence, or otherwise, find the total distance travelled by the tip of the pendulum when it has moved through half of the total accumulated angle.

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Answer

Half of the total accumulated angle is: 2602=130°\frac{260}{2} = 130° Distance travelled is: S=2π(1)×130360225extcmS = 2\pi(1) \times \frac{130}{360} ≈ 225 ext{ cm}

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