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Question
Math
Posted 10 months ago

An object is attached by a string to the end of a spring. Fang throws the object upwards and starts a stopwatch at t=0t=0 seconds. The object starts oscillating vertically in a periodic way that can be modeled by a trigonometric function.

The object's average height is 20 cm-20 \mathrm{~cm} (measured from the top of the spring). It first achieves that average height on the way up at t=0.2t=0.2 seconds, and then again every 2 seconds. The object's maximum and minimum heights are each 5 cm5 \mathrm{~cm} from its average height.

Find the formula of the trigonometric function that models the height HH of the weight tt seconds after Fang started the stopwatch. Define the function using radians.
H(t)=
H(t)=

\square
What is the height of the object after 0.6 seconds? Round your answer, if necessary, to two decimal places.
\square cm\mathrm{cm}
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Answer from Sia
Posted 10 months ago
Solution by Steps
step 1
To find the trigonometric function that models the height HH of the weight over time, we need to determine the amplitude, period, phase shift, and vertical shift
step 2
The amplitude is the maximum deviation from the average height, which is 5 cm5 \mathrm{~cm}
step 3
The period is the time it takes for one complete oscillation, which is 22 seconds. Since the function will be in terms of radians, we use the relationship T=2πωT = \frac{2\pi}{\omega} to find the angular frequency ω\omega
step 4
Solving for ω\omega, we get ω=2πT=2π2=π\omega = \frac{2\pi}{T} = \frac{2\pi}{2} = \pi
step 5
The phase shift is determined by the time it first reaches the average height on the way up. Since this occurs at t=0.2t = 0.2 seconds, the phase shift is 0.20.2 seconds to the right. In terms of ω\omega, the phase shift is ω5=π5\frac{\omega}{5} = \frac{\pi}{5}
step 6
The vertical shift is the average height, which is 20 cm-20 \mathrm{~cm}
step 7
Combining these values, the trigonometric function is H(t)=5cos(πtπ5)20H(t) = 5 \cos(\pi t - \frac{\pi}{5}) - 20
step 8
To find the height of the object after 0.60.6 seconds, we substitute t=0.6t = 0.6 into the function
step 9
Calculating H(0.6)=5cos(π0.6π5)20H(0.6) = 5 \cos(\pi \cdot 0.6 - \frac{\pi}{5}) - 20
step 10
Simplifying the cosine term, we get H(0.6)=5cos(3π5π5)20=5cos(2π5)20H(0.6) = 5 \cos(\frac{3\pi}{5} - \frac{\pi}{5}) - 20 = 5 \cos(\frac{2\pi}{5}) - 20
step 11
Using a calculator, we find that cos(2π5)0.309\cos(\frac{2\pi}{5}) \approx 0.309
step 12
Therefore, H(0.6)50.3092018.55 cmH(0.6) \approx 5 \cdot 0.309 - 20 \approx -18.55 \mathrm{~cm}
[1] Answer
H(t)=5cos(πtπ5)20H(t) = 5 \cos(\pi t - \frac{\pi}{5}) - 20
H(0.6)18.55 cmH(0.6) \approx -18.55 \mathrm{~cm}
Key Concept
Modeling periodic motion with trigonometric functions
Explanation
The trigonometric function for the height of the weight over time is determined by the amplitude, period, phase shift, and vertical shift. The height at a specific time is found by substituting the time into the function.

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