Sinusoidal Functions

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AP Precalculus › Sinusoidal Functions

Questions 1 - 9
1

A Ferris wheel height is $h(t)=10\cos\left(\frac{\pi}{12}t+\frac{\pi}{3}\right)+12$, with $t$ in minutes. The amplitude is the wheel radius, and the midline is the axle height. The phase shift indicates when the rider reaches the top relative to $t=0$. Using the given function, determine the phase shift of the function and explain its significance.​

4 minutes right; the cycle starts later than $t=0$

12 minutes left; the cycle starts earlier than $t=0$

4 minutes left; the cycle starts earlier than $t=0$

$\frac{\pi}{3}$ minutes right; the cycle starts later

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models Ferris wheel height h(t) = 10cos(πt/12 + π/3) + 12, where the phase shift determines when the cosine reaches its maximum. Choice A is correct because the phase shift is calculated as -C/B = -(π/3)/(π/12) = -4 minutes, meaning the cycle starts 4 minutes earlier than t = 0 (shifts left). Choice B is incorrect because it misinterprets the positive coefficient π/3 as causing a rightward shift, often a result of sign confusion. To help students: Practice calculating phase shift from the form cos(Bx + C) as -C/B. Encourage careful attention to signs when determining shift direction. Watch for: Sign errors in phase shift calculations, and confusion about positive C causing leftward shift.

2

A Ferris wheel height is given by $h(t)=14\cos!\left(\frac{\pi}{30}t-\frac{\pi}{3}\right)+16$, with $t$ in seconds. The amplitude is $14$ feet and the vertical shift is $16$ feet. The seat oscillates between $30$ feet and $2$ feet. The phase shift moves the first maximum away from $t=0$. Using the given function, determine the phase shift of the function and explain its significance.

$\frac{\pi}{3}$ seconds right; units stay radians

$10$ seconds left; peaks occur earlier

$30$ seconds right; period increases

$10$ seconds right; peaks occur later

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function h(t) = 14cos(πt/30 - π/3) + 16 can be rewritten as 14cos(π(t-10)/30) + 16, revealing a phase shift of 10 seconds to the right. Choice A is correct because factoring out π/30 from the argument gives π/30(t - 10), showing the horizontal shift is 10 seconds right, meaning peaks occur 10 seconds later. Choice D is incorrect because it interprets π/3 as the phase shift without converting to time units, often a result of not completing the factorization. To help students: Practice rewriting functions in the form f(B(t-h)) to find phase shift h. Encourage checking units to ensure the phase shift makes physical sense.

3

Average monthly temperature is modeled by $M(t)=12\cos!\left(\frac{2\pi}{12}(t-7)\right)+15$, with $t$ in months and $t=1$ as January. The amplitude is $12$°C and the vertical shift is $15$°C. The model peaks in midsummer and bottoms in midwinter. The period is one year, matching seasonal repetition. Based on the scenario, determine the phase shift of the function and explain its significance.

$7$ months right; peak shifts to August

$15$ months right; peak shifts to April

$7$ months left; peak shifts to December

$12$ months left; peak shifts to January

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models monthly temperature M(t) = 12cos(2π(t-7)/12) + 15, where the (t-7) term indicates a horizontal shift of 7 units to the right. Choice A is correct because it accurately identifies the phase shift as 7 months right, meaning the peak temperature shifts from January (t=1) to August (t=8), which aligns with real-world summer temperatures. Choice B is incorrect because it misinterprets the negative sign in (t-7) as a leftward shift, often a result of confusion about how horizontal transformations work. To help students: Practice rewriting functions in the form f(t-h) to identify rightward shifts of h units. Encourage connecting the mathematical shift to the physical meaning in context.

4

A sound wave’s displacement is $y=0.8\sin(440\pi t)+0$, where $t$ is seconds. The amplitude controls loudness, and the period controls pitch through frequency. The midline is zero displacement, and crests represent maximum compression. Using the given function, what is the period of the sinusoidal function described?​

$\frac{1}{440}$ seconds

$\frac{1}{220}$ seconds

$2\pi$ seconds

$440\pi$ seconds

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models a sound wave's displacement y = 0.8sin(440πt) + 0, where the coefficient 440π determines the period. Choice B is correct because it accurately calculates the period using the formula period = 2π/B, where B = 440π, giving period = 2π/(440π) = 1/220 seconds. Choice A is incorrect because it assumes the period is 1/440 seconds, often a result of confusing frequency with period. To help students: Practice distinguishing between period and frequency (frequency = 1/period). Encourage understanding that larger B values create shorter periods. Watch for: Confusion between period and frequency, and errors in simplifying the period formula.

5

A seasonal temperature model is $T(m)=9\sin!\left(\frac{2\pi}{12}m-\frac{\pi}{3}\right)+11$, with $m$ in months. The amplitude is $9$, and the vertical shift is $11$, representing the annual mean. The phase shift determines when the curve crosses its midline in spring. The period stays $12$ months, matching the yearly cycle. Using the given function, determine the phase shift of the function and explain its significance.

Shift right 4 months; maximum occurs 4 months later.

Shift right 2 months; midline crossing occurs 2 months later.

Shift left 4 months; minimum occurs 4 months earlier.

Shift left 2 months; midline crossing occurs 2 months earlier.

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models seasonal temperature T(m) = 9sin(2πm/12 - π/3) + 11, where the phase shift is found by solving 2πm/12 - π/3 = 0, giving m = 2 months. Choice A is correct because it accurately calculates a right shift of 2 months, meaning the midline crossing occurs 2 months later than without the shift, verified by the negative phase angle -π/3. Choice C is incorrect because it doubles the phase shift and confuses midline crossing with maximum occurrence. To help students: Practice solving Bx + C = 0 to find phase shifts. Visualize sine starting at midline going up, then shifting based on the phase.

6

A harbor tide height (meters) follows $H(t)=2.6\sin!\left(\frac{\pi}{6}t\right)+3.1$, where $t$ is hours after midnight. The midline is $3.1$ meters, and the tide oscillates symmetrically about this level. The amplitude represents half the high-to-low tidal range. Using the given function, calculate the amplitude of the function given in the scenario.

$5.2$ meters

$3.1$ meters

$1.55$ meters

$2.6$ meters

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models harbor tide height H(t) = 2.6sin(πt/6) + 3.1, where the amplitude A = 2.6 meters represents half the total tidal range. Choice A is correct because it accurately identifies the coefficient of the sine function as the amplitude, which is 2.6 meters, representing the maximum deviation from the midline of 3.1 meters. Choice B is incorrect because it doubles the amplitude, confusing it with the total tidal range from high to low tide. To help students: Emphasize that amplitude is always the coefficient in front of the sine or cosine function, not the total range. Practice identifying A, B, C, and D values directly from the function form.

7

A Ferris wheel seat height follows $h(t)=18\cos\left(\frac{\pi}{20}t\right)+20$, with $t$ in minutes. The wheel rotates steadily, starting at maximum height at $t=0$. The amplitude is the radius, and the vertical shift is the axle height. Based on the scenario, what is the period of the sinusoidal function described?​

2\pi minutes

10 minutes

20 minutes

40 minutes

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models a Ferris wheel's height h(t) = 18cos(πt/20) + 20, where the coefficient of t inside the cosine function determines the period. Choice B is correct because it accurately calculates the period using the formula period = 2π/B, where B = π/20, giving period = 2π/(π/20) = 40 minutes. Choice C is incorrect because it assumes the coefficient π/20 is the period itself, often a result of confusing the period formula. To help students: Practice identifying B in the general form and applying the period formula 2π/B. Encourage visualization of one complete rotation taking 40 minutes. Watch for: Confusion between the coefficient and the actual period, and misinterpretation of the period formula.

8

Tidal height is $y=1.8\sin\left(\frac{\pi}{4}x\right)+3.2$, where $x$ is hours after midnight. The amplitude measures half the tidal range, and the vertical shift gives average sea level. High tide corresponds to the maximum value of the function. Using the given function, what is the maximum value and when does it occur?​

5.0 at $x=4$

1.8 at $x=2$

3.2 at $x=0$

5.0 at $x=2$

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models tidal height y = 1.8sin(πx/4) + 3.2, where the maximum occurs when sine equals 1. Choice A is correct because the maximum value is 1.8(1) + 3.2 = 5.0 meters, and this first occurs when πx/4 = π/2, solving for x gives x = 2 hours. Choice D is incorrect because it miscalculates when the sine function first reaches its maximum, often a result of solving for the wrong angle. To help students: Practice finding when sin(Bx) = 1 by setting Bx = π/2. Encourage finding the first occurrence of the maximum within one period. Watch for: Errors in solving for x, and confusion about which value of x gives the first maximum.

9

The ocean tide height is modeled by $y=2.5\sin\left(\frac{\pi}{6}x-\frac{\pi}{3}\right)+4$, where $x$ is hours after midnight. The midline represents average sea level, and peaks represent high tide. The amplitude measures half the tidal range, and the period gives the time between successive highs. Using the given function, calculate the amplitude of the function given in the scenario.​

4 meters

1.5 meters

2.5 meters

5 meters

Explanation

This question tests AP Precalculus skills, specifically understanding and application of sinusoidal functions. Sinusoidal functions, such as y = A sin(Bx + C) + D, model periodic phenomena, where A represents amplitude, B affects period (2π/B), C indicates phase shift, and D is the vertical shift. In this scenario, the function models ocean tide height y = 2.5sin(πx/6 - π/3) + 4, where the coefficient 2.5 in front of the sine function represents the amplitude. Choice C is correct because it accurately identifies the amplitude as 2.5 meters, which represents half the total tidal range (the difference between high and low tide). Choice B is incorrect because it confuses the vertical shift (4) with the amplitude, often a result of misunderstanding which parameter controls wave height. To help students: Practice identifying A as the coefficient directly in front of the sine or cosine function. Encourage visualization of amplitude as the distance from midline to peak. Watch for: Confusion between amplitude and vertical shift, and misinterpretation of the amplitude's physical meaning.