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Homework Help: Can someone check my answers on these kinematics questions?

  1. Sep 25, 2005 #1

    dnt

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    I think im doing them right but they dont match the answers that were supplied to me - i think the

    answers may have typos.

    1. A bike accelerates uniformly from rest to a speed of 7.10 m/s over a distance of 35.4 m.

    Determine the acceleration of the bike.


    my answer: I used the formula v^2 = vo^2 + 2ad and got a = .712 m/s^2



    2. A car traveling at 22.4 m/s skids to a stop in 2.55 s. Determine the skidding distance of the

    car (assume uniform acceleration).


    my answer: I solved for acceleration first (-8.78 m/s^2) then used d=Vot + 1/2(a)t^2 to get

    d = 28.57 m.



    3. A bullet is moving at a speed of 367 m/s when it embeds into a lump of moist clay. The bullet

    penetrates for a distance of 0.0621 m. Determine the deceleration of the bullet when moving into

    the clay.


    my answer: I used the formula v^2 = vo^2 + 2ad and got a = -1.08 x 10^6 m/s. (my issue

    here is that the answer should be negative, not positive. right?)



    4. A dragster accelerates to a speed of 112 m/s over a distance of 398 m. Determine the

    acceleration of the dragster.


    my answer: Once again I used the formula v^2 = vo^2 + 2ad (with Vo = 0; at least I assume

    that is true) and got a = 15.76 m/s^2.



    I think my equations and answers are right but if not, can someone help me out and correct me where I have made mistakes.
    Thanks.
     
  2. jcsd
  3. Sep 25, 2005 #2
    The reasoning to all of your answers makes sense, I did not check the actuak numeric values to the answers though.
     
  4. Sep 26, 2005 #3

    dnt

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    can someone else check the answers to make sure they are correct? thanks.
     
  5. Sep 26, 2005 #4

    VietDao29

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    Homework Helper

    #1, you got it right.
    #2, wrong a little bit, it's exactly : d = 28.56 m (not d = 28.57 m). But 0.01 m would be negligible.
    #3 is correct exept that it should be a = -1.08 x 106 m/s2, (not -1.08 x 106 m/s) :).
    #4 is also correct.
    Viet Dao,
     
  6. Sep 26, 2005 #5

    dnt

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    thanks viet.
     
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