Sinusoidal Word Problems

[skeske1234]

I have finished the questions for the following, but could someone please check to see if my answers are right because there are no answers for these questions since it's a sheet that my teacher gave us.

Ok, just let me know where my errors are and what is the correct answer if applicable.

Thank you in advance!

1. Write a sinusoidal function for the function with a period of 6. The function has a max of 3 at x=2 and a low point of -1.

My answer: y=2sin[(pi/3)(x)] +1

2. Write a sinusoidal function for the function with a period of 5. The function has a max of 7 at x=1.

My answer: y=3.5sin[(2pi/5)(x+0.25)]

3. When you board a Ferris wheel your feet are 1 foot off the ground. At the highest point of the ride, your feet are 99 feet above the ground. It takes 30 seconds for the ride to complete one revolution. Write a sinusoidal function for your height above the ground at t seconds after the ride starts.

My answer: y=49sin[(pi/15)(x-30)+50]

4. At high tide the water level at a particular boat dock is 9 feet deep. At low tide, the water is 3 feet deep. On a certain day the low tide occurs at 3 am and the high tide occurs at 9 am. Find an equation for the height of the tide at time t.

My answer: y=3cos(pi/12x)+6

5. Jessie has a pulse rate of 73 beats per minute and a blood pressure of 121 over 85. If Jessie's blood pressure can be modeled by a sinusoidal function, find an equation of this sinusoid.

My answer: y=0.7sin(146pix)

6. As the paddlewheel turned, a point on the paddle blade moved back in such a way that its distance, d, from the water's surface was a sinusoidal function of time. When a stopwatch read 4 seconds the point was at it's highest, 16ft about the water's surface. The wheel's diameter was 18 ft. and it completed a revolution every 10 second.

My answer: y=9sin[pi/5(x-1.5)]+7

7. The number of sunspots counted in a given year varies periodically from a minimum of about 1 per year to about 110 per year. Between the maximums that occurred in the years 1750 and 1948, there were 18 complete cycles.

my answer: y=54.5sin(2pi/11x)+55.5

8. You seek treasure that is buried in the side of a mountain. The mountain range is a sinusoidal cross section. The valley to the left is filled with water to a depth of 50 meter, and the top of the range is 150 meters above water level. You set up an x-axis at water level and a y axis 200 meters to the right of the deepest part of the water. The top of the mountain is at x=400 meter.

my answer: y=225sin[pi/100(x-200)]+175

9. A creatures body temperature is varying sinusoidally with time. 35 minutes after they start timing it reaches a high of 120 degrees F and a 20 minutes after that its next low is 104 degrees F.

my answer: y=8sin[pi/20(x-25)]+112

10. A ferris wheel is 50 ft in diameter, with the center 60 ft above the ground. You enter from a platform at the 3oclock position. It takes 80 sec to complete one revolution. Find the equation that gives you your height when you entered the ferris wheel above the ground at t time. (t=0 when you entered).

my answer: y=-25sin(pi/40x)+35


Okay, thanks again for whoever who helps! I really really appreciate it!

 

[arthur ohlsten]

the first one is wrong
the function oscilates around y=[3-1]/2 or y=1

y=1+ 2 sin 2pi t /6 answer

the max when 2 pi t= pi/2, and is 2+1
the minimum is when 2pit = 3pi/2 and is -1
at t=0 we have 1+2 sin 0
at t=6 we have 1+2sin 2pi

please reenter the remaining problems, each one as a separate problem
Arthur

 

[mmm4444bot]

I regret that I cannot locate my motivation for checking these, right now.

Perhaps, you'll find that graphing your results will help you to confirm your own answers, on some of these.

For example, you can see from the graph that your phase shift is off on the first exercise, as noted by Arthur.

If you need a graphing machine, here's a virtual one. (Coordinates display for the tip of your mouse pointer; point to the first maximum in Quadrant I, and you'll see that x is not 2 there.) CLICK HERE to see the graph of your first result at a web site that plots graphs.

I also note that some of your other exercises may be checked by substituting given values into your equation, followed by arithmetic, to verify that the equation is true.

Lastly, I'm sure that Arthur meant to suggest that IF you need additional help on any of these individual exercises, THEN please start a new discussion (i.e., thread) for each. It's more organized than having this thread turn into 20 screenfuls.