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What is the distance travel by the ball when the time is 1 sec?

  1. Feb 13, 2008 #1
    i throw a ball upwards
    reach highest point at 3secs later
    what is the distance travel by the ball when the time is 1 sec?
    take g = 10m/s^2



    another is
    a car deccelerates from 20m/s at a rate of 2ms^2...
    how long does it take to reach 100m

    im trying to explain it to my younger brother. but im not sure how to. can anyone help?
     
  2. jcsd
  3. Feb 13, 2008 #2

    Hootenanny

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    Really? Well, what has 'younger brother' tried to do already? Has 'he' looked at his class notes or text?
     
  4. Feb 13, 2008 #3
    for the first question.

    i manage to find the initial speed which was 30m/s. i derive it through the formulae

    (v1-v2)/t = acc. so i drew out the v/t graph, and calcuate the area under graph when the time is 1sec. i got 25m.

    the 2nd question. i use the same formulae (v1-v2)/t =acc. to find out the time. which is 10secs. if i calculate the area under graph, it's 100m. which is what the question is asking us to find.

    is the method i used viable? or is there a simpler method for people to understand better?
     
  5. Feb 13, 2008 #4

    Hootenanny

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    Yes, your methods are valid. However, a much more straightforward approach would be to use kinematic equations.
     
  6. Feb 14, 2008 #5
    i got another query. can i just find out the average speed for both of the question. and then use it to find the answer?

    i cant get it for the 1st question. but i can get the answer for the 2nd one.
     
  7. Feb 14, 2008 #6

    Hootenanny

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    Yes, since the acceleration in both cases in constant, you can use the average velocity to compute the answer.
    If you post your attempts perhaps we can show you where your going wrong.
     
  8. Feb 14, 2008 #7
    for the 1st question.:

    i calculate out the initial speed which was 30m/s. and drew out the v/t graph.
    using the graph i found out that the total distance travelled during the 3secs is 45m.
    so the average speed would be 45/3 which is 15m/s.

    i need to find out the distance travelled in 1sec. which would be 15m.
    but the answer is 25m.
     
  9. Feb 14, 2008 #8
    anyone?
     
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