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Basic Physics Question-But I'm stuck!

  1. Jan 24, 2014 #1
    So as I have been completing my physics homework, there is one question I can not get passed. However I feel as if I already have the answer. The question is: What is the speed of the car 10.0 s after it begins its motion if it continues to move with the same acceleration?

    The original problem states that:A certain automobile manufacturer claims that its deluxe sports car will accelerate from rest to a speed of 44.5 m/s in 8.90 s.

    From what I have worked out the answer is 22.5m/s but it keeps telling me I am wrong. Any help would be greatly appreciated. Thank you!

    -Jake
     
  2. jcsd
  3. Jan 24, 2014 #2
    Well, without giving it all away, do you think that is a reasonable answer? (As you have stated the question, it is not.)
     
  4. Jan 24, 2014 #3
    I think it would be helpful if we could see the work you've done, that way we can identify where exactly the mistake is!
     
  5. Jan 24, 2014 #4
    So I went ahead and found the distance by multiplying (1/2)*44.5*10 which came out as 225. I then divided that by 10 which is the time interval the question wants me to identify. I get 22.5 which is obviously wrong for some reason, but I am still stuck nonetheless.
     
  6. Jan 24, 2014 #5
    Your numbers are slightly off (even for what you are doing), but my main objection is this: the question tells you that the car accelerates from rest with the same acceleration all the time - yet you claim that it will travel slower after 10 seconds than it did after 8.9 seconds.
     
  7. Jan 25, 2014 #6
    No…at 8.9 seconds it is traveling at the same speed.
     
  8. Jan 25, 2014 #7
    Maybe I am reading this completely wrong then? "A certain automobile manufacturer claims that its deluxe sports car will accelerate from rest to a speed of 44.5 m/s in 8.90 s." To me, that certainly sounds like the car travels at 0 m/s in the beginning, and at 44.5 m/s after 8.90 s.
     
  9. Jan 25, 2014 #8
    Uh, I'm sorry, I really don't know what I am doing with this problem. I keep getting confused with its acceleration and speed. Could you point me in the direction you would go for this problem?
     
  10. Jan 25, 2014 #9
    Okay nevermind, it was just 5*10.
     
  11. Jan 25, 2014 #10
    And you understand right, correct? The average acceleration of the car is ##5 \frac{m}{s^2}##, and multiplying that by the time given (ten seconds) gives you the velocity at that time.
     
  12. Jan 25, 2014 #11
    Got it. Thanks.
     
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