Results 1 to 8 of 8

Math Help - Finding a formula...

  1. #1
    Junior Member
    Joined
    May 2007
    Posts
    56

    Finding a formula...

    13. The distance, D, travelled by a particle is directly proportional to the square of the time, t, taken.

    When t = 40, D = 30

    (a) Find a formula for D in terms of t.
    (b) Calculate the value of D when t = 64
    (c) Calculate the value of t when D = 12
    Give your answer correct to 3 sig fig.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by Danielisew View Post
    13. The distance, D, travelled by a particle is directly proportional to the square of the time, t, taken.

    When t = 40, D = 30

    (a) Find a formula for D in terms of t.
    (b) Calculate the value of D when t = 64
    (c) Calculate the value of t when D = 12
    Give your answer correct to 3 sig fig.
    Hint
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,939
    Thanks
    338
    Awards
    1
    Quote Originally Posted by Danielisew View Post
    13. The distance, D, travelled by a particle is directly proportional to the square of the time, t, taken.

    When t = 40, D = 30

    (a) Find a formula for D in terms of t.
    (b) Calculate the value of D when t = 64
    (c) Calculate the value of t when D = 12
    Give your answer correct to 3 sig fig.
    From the problem statement D = kt^2 where k is some constant.

    When t = 40, D = 30. So:
    D = kt^2

    30 = k(40)^2

    k = \frac{30}{1600} = \frac{3}{160}

    You should be able to do the rest.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    May 2007
    Posts
    56
    Quote Originally Posted by topsquark View Post
    From the problem statement D = kt^2 where k is some constant.

    When t = 40, D = 30. So:
    D = kt^2

    30 = k(40)^2

    k = \frac{30}{1600} = \frac{3}{160}

    You should be able to do the rest.

    -Dan
    What would you put for part (a) the formula?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by Danielisew View Post
    What would you put for part (a) the formula?
    D = \frac {3}{160}t^2

    Just replace k in the general formula Dan showed you
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Junior Member
    Joined
    May 2007
    Posts
    56
    WAT THE.. I am confused :S
    Follow Math Help Forum on Facebook and Google+

  7. #7
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by Danielisew View Post
    WAT THE.. I am confused :S
    Did you look at the hint I gave you?

    By definition, two quantities are directly proportional if one is a constant times the other. so saying that D is proportional to t^2 is saying that

    D = k t^2

    That is the general formula for proportional quantities. Now to answer specific questions, we need to know exactly what the constant is. Dan used the two given values of D and t to find k, so now we just replace that k in the general formula.

    Since we found that k = \frac {3}{160}, we can plug it in to the formula, so:

    D = \frac {3}{160} t^2

    Now we can use this to answer all the questions. Since now we have only two unknowns, it means that if we are given one of the unknowns, we can easily solve for the other
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Junior Member
    Joined
    May 2007
    Posts
    56
    oh, ok thanks for explaining it. I understand it better now.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Finding a formula
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: November 9th 2010, 01:36 AM
  2. Replies: 1
    Last Post: April 26th 2010, 07:16 PM
  3. Finding the formula
    Posted in the Calculus Forum
    Replies: 2
    Last Post: November 7th 2009, 06:24 AM
  4. finding formula with max and min
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: March 18th 2008, 01:51 PM
  5. Finding a Formula
    Posted in the Advanced Math Topics Forum
    Replies: 3
    Last Post: October 24th 2006, 11:35 PM

Search Tags


/mathhelpforum @mathhelpforum