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Acceleration Problems

  1. Jan 28, 2010 #1
    The first one is
    It takes 40sec for a car at rest to reach a velocity of 50 m/s. What is the car's initial velocity?
    a. 0 m/s
    b. 1.25 m/s
    c. 1.25 m/s2
    d. 50 m/s
    e. 50 m/s2
    I think the equation is a=v(final)-v(intial)/t
    but it can't be because doesn't a(acceleration)= m/s2?
    so there for you don't have the number acceleration to plug in??
    Also I think I think v(final) is 50 m/s... and I don't knbow but if something
    is at rest then wouldn't that be v(intial)?? Please help!!!! I am so confused! OMG
    I really need to know this for a upcoming test

    The next one is.
    It takes 40sec for a car at rest to reach a velocity of 50 m/s. What is the car's acceleration?
    I know the answer for this one but what is confusing me is that I have to choices for this answer and they are
    A. 1.25 m/s
    B. 1.25 m/s2

    could you explain to me which one is right and how did you come to get that
    this is how I solved this problem

    I used a=v(final)-v(initial)/t(time)
    The v(final) is 50m/s and the v(initial) is 0 because the car started at rest.
    and the t is 40 (because its in seconds
    I subtracted 50-0 then divded it by 40.

    Last but not least:
    A car starts from rest has a constant acceleration of 4m/s2. In the first 3s the car travels
    a. 6m
    b. 12m
    c. 18m
    d. 172m
    I really do not understand this one. Do you use the acceleration formula.

    PLEASE HELP!! I went to tutoring at my university and they didn't know how to do them either! So help me smart people lol.

    Thank you in advance!
     
  2. jcsd
  3. Jan 29, 2010 #2

    Lok

    User Avatar

    1. At rest means just that, this seems like a trick question but it isn't, you are supposed to know that without doubts. V=0

    2. HINT! The International units of measure for acceleration are ... ?

    3. The relevant formula is the acceleration formula x=Vinital*t+1/2a(tpower2) (t squared for all things.)
    Again the initial speed is like in the first.
     
  4. Jan 29, 2010 #3

    Lok

    User Avatar

    Now i see you didn't understand the second m/s2 m/s

    m/s means how many meters per second an object gains (travels). than means speed

    m/s^2 means how much speed(m/s) per second an object gains (acceleration).

    You used a formula. Maybe something like a=v/t well this means that a=m/s/s=m/s^2 (for best results keep in mind that v=m/s )
     
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