More related rates.

Heyy, its me again. So last night I asked a related rate question, and I think I still don't get it. I tried it a few differnt ways and I think I'm just missing something...I don't think a speed of a rocket can be 0.018km/hr:S. So heres what happened:
A camera, located 2 km from the launch pad, is tracking the rocket that is fired straight up. When the height of the rocket is 20 km, the camera is rotating at the rate of 1/200 radians per second. What is the speed of the rocket at that instant? Give your answer in km/sec.
I drew a picture which is a triangle. And I know that tan theata =20/2 (I think), and we know dtheata/dt = 1/200 radians. We are looking for dh/dt. So tan theata =h/2 so the derviative is sec^2 theata dtheata/dt =1/2dh/dt which means that 2(1/cos^2theata)(dtheata/dt)=dh/dt
So when I do this out, I get 0.018 and I don't think that's right. I think I'm missing something important and I can't figure out what it is.

And also, I have one more question. Me and my friends worked on this for liek 2 hours, we all did the same thing and got the smae answer no matter waht we did but it says its wrong so I don't know what is going wrong.
A girl 6 ft tall is walking away from a streetlight. The streetlight is attached to a pole that is 16 feet tall, and is generating a shadow. If the tip of the girl's shadow is moving at 5 ft/sec, how fast is she walking? Give your answer in ft/sec.

The answer I got was -3, using similar triangles. And we also did it a differnt way and got 8.3 but that's also wrong.

Thanks ahead of time, I know its alot, I'm sooo frsutrated.

Here you know the angle, and you are given dTheta/dt. You are looking for dh/dt

You know TanTheta=h/2, and you know dtheta/dt when h=2-

start with TanTheta=h/2
take the derivative with respect to time. It will come out rather simply.

sec^2theta * dTheta/dt = 1/2 dh/dt

dh/dt= 2*sec^2Theta dT/dt
= 2* (h^2+ 3)^1/2 /2 * 1/200
= 2* (400+ 3)^1/2 /2 * 1/200
=appx .1 km/sec check my work.

let the distance x be the distance from the tall lamp to the end of the shadow.
16/x= 6/(x-D) where D is the distance from the lamp to the girl. This is from similar triangles.

16(x-D)= 6x
16 dx/dt - 16dD/dt= 6 dx/dt
given dx/dt is 5ft/sec, dD/dt is the unknown.


Okay, so heres where I get lost:
= 2* (h^2+ 3)^1/2 /2 * 1/200
= 2* (400+ 3)^1/2 /2 * 1/200
=appx .1 km/sec check my work.
Where did you get the h^2 +3 ^1/2
And what value is h to make it 400?

  1. 👍 0
  2. 👎 0
  3. 👁 104
asked by Tracy

Respond to this Question

First Name

Your Response

Similar Questions

  1. english

    Question #1 Is the following sentence written correctly? Yes or no? 1. “Hey,” he asked, “who are they?” 2. “No,” she said “that is not painful.” 3. “His mother, he said, “is taking night classes”. 4.

    asked by Anonymous on September 24, 2015
  2. algebra

    During a study of auto accident,the highway safety council found that 60%of all accident occur at night,52%are alcohol-related,and 37% occur at night and are alcohol related :a)What is the probability that an accident was

    asked by ankit on May 7, 2016
  3. chemistry

    if the concentration of all the reactants doubled, what works happen to the rate I know the reaction rate would increase, but in a previous example it asked the question and the answer was that the rate increases by 16 and I can't

    asked by alyssa on March 10, 2015
  4. English

    Thank you very much! Just one more thing. Should I evaluate the following sentence a mistake? 1) The journalist asked where I was going to sing ...... (istead of "asked me") The officer asked if I could show him my permit (instead

    asked by Henry on March 5, 2012
  5. english

    Question #1 Is the following sentence written correctly? Yes or no? 1. “Hey,” he asked, “who are they?” 2. “No,” she said “that is not painful.” 3. “His mother, he said, “is taking night classes”. 4.

    asked by Anonymous on September 24, 2015
  6. science

    how long does a teenager need to sleep at night?? my teacher asked this question and if you get it right, you get 2 extra points on a test, so please help me!!

    asked by hannah on October 17, 2011
  7. Chemistry

    CoCl2 is a compound that is blue when it is dehydrated and pink when in its hydrated form. I have seen a solution of CoCl2 used to paint a coloring book type figure (on paper). This is hung outside and gives a blue color when the

    asked by DrBob222 on November 16, 2006
  8. Physics

    Hello I am trying to solve this physics problem related to effusion of gases. The following data is given and I am asked to calculate the rate of effusion The data given; depth/thickness (t) Surface area (A) diffusion coefficient

    asked by Sam on December 15, 2012
  9. english

    what is an interjection? Try www.dictionary.com what key would you use forlesson7-1 homework helper online I wish someone would answer my question the telling me to look it up!!!!!!!!!!! what question????????????????????? what

    asked by julie on September 8, 2006
  10. College Algebra

    According to data from the National Vital Statistics Report, the marriage rate (marriages per 1000) can be described by y=-0.146x+11.074, where x is the number of years after 1980. For what years does this model indicate that the

    asked by Math Sucks on January 8, 2015

More Similar Questions