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Checking Vectors

  1. Feb 6, 2010 #1
    1. The problem statement, all variables and given/known data
    I've done this problem please check.
    A bicyclist has a uniform acceleration of 2.30ms-2. What distance will he need to travel in order to attain a velocity of 21ms-2 if he started at rest?


    2. Relevant equations
    Hopefully this is the equation:
    v2=u2+2as
    i have rearranged this in my problem.

    3. The attempt at a solution
    v2-u2/2a
    212-2.302/2*2.30
    =94.72m

    Please check the working and the final measrement (94.72m)
    thanks
     
  2. jcsd
  3. Feb 6, 2010 #2
    v = v_0 + a*t, and
    x = x_0 + v_0*t + .5*a*t^2, so in your case

    v = a*t, and
    x = .5*a*t^2, two equations in two unknowns.
     
  4. Feb 15, 2010 #3
    thanks
     
  5. Feb 17, 2010 #4

    tiny-tim

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    uhh? :confused:

    v2=u2+2as was the correct formula​
     
  6. Feb 19, 2010 #5
    I find it more easy to memorize one formula and then manipulate as needed. It sticks with you longer?
     
  7. Feb 19, 2010 #6

    tiny-tim

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    Hi Spinnor! :smile:

    I strongly recommend against that.

    In most problems, one of the three standard constant acceleration formulas will do the job immediately, and so they should all be learnt.

    In an examination, you have to show your calculations, and it wil become obvious either that you don't know one of the formulas, or that you do know, but you've made the answer longer by choosing the wrong one … either way, you'll lose marks. :redface:
     
  8. Feb 19, 2010 #7
    Learn the formulas and not where they come from and in a year you will remember little. Learn the basic formulas and maybe a year from now those looking for help could still do the problems they come here for help?

    To each his own.
     
  9. Feb 19, 2010 #8
    Either way I am still hopeless with all the formulas. I've been taught to get the basic equation v2=u2+2as and derive it to get the other equations.
     
  10. Feb 19, 2010 #9

    tiny-tim

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    Learn all three equations. :wink:

    They're surprisingly easy to remember. :smile:
     
  11. Feb 19, 2010 #10
    Yeah I know, I do prefer that. That is what I have done :)
     
  12. Feb 19, 2010 #11

    vela

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    To answer your original post, your answer is wrong.

    You need to understand what the variables in the formulas mean. In the equation you used, what does u represent? Does it make sense to set u=2.30 m/s^2 as you did?
     
  13. Feb 19, 2010 #12
    u should equal to 0 right.
     
  14. Feb 19, 2010 #13
    Your methodology is correct, except you need to rethink what the initial velocity is.
     
  15. Feb 20, 2010 #14

    tiny-tim

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    right! :biggrin:
     
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