Results 1 to 15 of 15

Math Help - some math problems

  1. #1
    Junior Member
    Joined
    Nov 2006
    Posts
    73

    some math problems

    1.Suppose p varies inversely as the square root of q. If p=-7 when q=9, what is p if q is 6?
    p=_____

    2.The stopping distance d of an automobile is directly proportional to the square of its speed v. A car required 50 feet to stop when its speed was 80 miles per hour. Find a mathematical model that gives the stopping distance d in terms of its speed v.
    Your answer is d=_____
    Estimate the stopping distance if the brakes are applied when the car is traveling at 62 miles per hour.
    Your answer is_____.

    3.If the point is on the unit circle in quadrant IV, then y=___.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,186
    Thanks
    404
    Awards
    1
    Quote Originally Posted by badandy328 View Post
    1.Suppose p varies inversely as the square root of q. If p=-7 when q=9, what is p if q is 6?
    p=_____
    We know that
    p = (const)/sqrt(q)

    Using the first point we get:
    -7 = (const)/sqrt(9)

    Thus (const) = (-7)*sqrt(9) = (-7)*3 = -21

    Thus
    p = -21/sqrt(q)

    When q = 6:
    p = -21/sqrt(6)

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Oct 2005
    Posts
    36
    I'm going to do them in the order I think they are the easiest!

    3. If that point is on the unit circle centered at the origin then the distance to the origin from that point must be 1. So root(x + y) = 1

    16/25 + y = 1
    y = 9/25
    y = -3/5
    (y must be negative as you want the answer in the 4th quadrant)

    2.

    d = kv (where k is a constant)
    50 = k80
    50 = 6400k
    k = 1/320

    So the model is therefore d = v/320

    For the second part just put v = 62 into that equation.

    1. p = k/root(q)

    So -7 = k / root(9)
    So k = -+ 21

    Using this value of k : p = +-21 / root(6)

    Hope that helps.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,186
    Thanks
    404
    Awards
    1
    Quote Originally Posted by badandy328 View Post
    2.The stopping distance d of an automobile is directly proportional to the square of its speed v. A car required 50 feet to stop when its speed was 80 miles per hour. Find a mathematical model that gives the stopping distance d in terms of its speed v.
    Your answer is d=_____
    Estimate the stopping distance if the brakes are applied when the car is traveling at 62 miles per hour.
    Your answer is_____.
    d = (const)v^2

    So
    50 ft = (const)*(80 mi/h)^2

    So (const) = (50 ft)/(80 mi/h)^2 = 1/128 ft h^2/mi^2. (Note how strange this unit is. We need to remember that the formula we will be using converts an initial speed in mi/h to a stopping distance in ft.)

    Thus
    d = v^2/128.

    So for v = 62 mi/h, d = (62)^2/128 ft = 30.0313 ft.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Oct 2005
    Posts
    36
    Oops! I never even noticed the feet/miles issue. Darn.

    *slaps himself*
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Junior Member
    Joined
    Nov 2006
    Posts
    73
    Wow, i was really off in number 2. For the equation i got like d=d*v/v. lol thanks. The last one i need help in. I can't figure out that bow tie triangle thing.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,186
    Thanks
    404
    Awards
    1
    Quote Originally Posted by badandy328 View Post
    Wow, i was really off in number 2. For the equation i got like d=d*v/v. lol thanks. The last one i need help in. I can't figure out that bow tie triangle thing.
    What question is that? I don't see it.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Junior Member
    Joined
    Nov 2006
    Posts
    73
    Oh, I'm sorry. Number 3. this one:

    3.If the point is on the unit circle in quadrant IV, then y=___.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Junior Member
    Joined
    Oct 2005
    Posts
    36
    I answered that one at the top of my post. I messed up the second question, but I'm pretty sure I got question 3 right.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Junior Member
    Joined
    Nov 2006
    Posts
    73
    No it's apparently wrong. I got that same answer but without the negative. So it's not 3/5 or -3/5
    Follow Math Help Forum on Facebook and Google+

  11. #11
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,186
    Thanks
    404
    Awards
    1
    Quote Originally Posted by TheBrain View Post
    I answered that one at the top of my post. I messed up the second question, but I'm pretty sure I got question 3 right.
    You got it right. That's why I didn't post an answer for 3 myself.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  12. #12
    Junior Member
    Joined
    Nov 2006
    Posts
    73
    ok whatever. Thanks guys, your the best.
    Follow Math Help Forum on Facebook and Google+

  13. #13
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,186
    Thanks
    404
    Awards
    1
    Quote Originally Posted by badandy328 View Post
    No it's apparently wrong. I got that same answer but without the negative. So it's not 3/5 or -3/5
    What makes you think -3/5 is incorrect?

    -Dan
    Follow Math Help Forum on Facebook and Google+

  14. #14
    Junior Member
    Joined
    Nov 2006
    Posts
    73
    I put it in as an answer for my homework website and it says it is wrong.
    Follow Math Help Forum on Facebook and Google+

  15. #15
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    10,186
    Thanks
    404
    Awards
    1
    Quote Originally Posted by badandy328 View Post
    I put it in as an answer for my homework website and it says it is wrong.
    Hmmm.... Well, I won't often say this, but for this particular question I would say that the computer is wrong. If not, please let us know what your teacher/professor tells you is the correct answer.

    -Dan
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Two math problems.
    Posted in the Algebra Forum
    Replies: 4
    Last Post: December 15th 2010, 03:53 PM
  2. A few math problems.
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: January 12th 2010, 05:48 AM
  3. Need help with a few math problems
    Posted in the Advanced Algebra Forum
    Replies: 4
    Last Post: April 2nd 2008, 11:42 AM
  4. math problems
    Posted in the Algebra Forum
    Replies: 4
    Last Post: May 22nd 2006, 07:48 PM
  5. math problems
    Posted in the Algebra Forum
    Replies: 5
    Last Post: May 19th 2005, 03:52 PM

Search Tags


/mathhelpforum @mathhelpforum