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Can you verify my Physics work please?

  1. Feb 23, 2013 #1
    I am preparing for a physics test and i want to make sure what and how I am solving the review questions is correct because I have no answer key!Thank you in advance!

    2-You are driving in your car at a steady 80.0km/h. and you suddenly see a stop sign. You apply your breakes and stop after 60.0m(or 0.06km).

    a)How long did it take you to stop?
    What I did was find Vavg=0.5(80.0km/h + 0.0km/h) then using it in the equation of delta d=Vavg.*delta t and getting an answer of 0.0015h.

    b)What was your acceleration?
    What I did was using the formula V2^2=V1^2+2a(delta d) and I solved to get a= (to appropriate sig fig) -53300km/h^2


    3-During the span of 5.0s time interval an object begins at 5.0m/s, accelerates uniformly and ends at 20.0m/s.

    a) What is the average speed of the obect in this 5 s interval?
    What I did Vavg=0.5(20.0m/s + 5.0m/s)=12.5m/s

    b)What is the acceleration?
    What I did v2=v1+2a(t)
    20.0m/s=5.0m/s+2a(5.0s)
    a= 3.0m/s^2



    Thank you again!!
     
  2. jcsd
  3. Feb 23, 2013 #2

    mfb

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    2016 Award

    Staff: Mentor

    I would choose a different formula for 2b (you already know the velocity difference and the time), but that one is possible as well.
    m/s and m/s^2 would be more conventional units for the answers. I did not check the numbers, a computer can do this quicker.

    3 is fine.
     
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