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SO I have an Exam Tomorrow. Review Questions!

  1. Jun 18, 2008 #1
    Velocity, Acceleration, Displacement, Headache

    I have an exam tomorrow. Can you help me out with these physics questions? They are review questions that I am stuck on.

    1) Distance is 45 km and it took 3 seconds what is the speed. If the displacement is 7 km north what is the velocity?

    *I know the speed is 15km/s, but I don't get the velocity. (I know velocity = displacement over time).

    2) Draw a scale vector diagram to find the resultant displacement of the following scenario. A football is thrown 30 m north 85 degrees west. Then run 3 m north 10 degrees east. Finally kick 21 m east 80 degrees south.

    * I don't understand the degree part.

    3) A cart is accelerating at a rate of 0.6m/s(squared). After 7 seconds it is moving at 4.7m/s(sq). What was it's initial velocity.

    *I got 32.9, is that correct?

    4) A ball is rolling down a ramp from rest. How long will it take to reach a velocity of 6.0 m/s, if its acceleration is 1.5 m/s(sq)?

    * Really don't know where to start. Acceleration is velocity over time. So do I move it aaournd, so I have t=va? In which my answer should be 9?

    5) Instantaneous velocity at 65 m/s? (From question 4)

    I'd like to know how to do each of these questions, as in my science teacher cared more about his baby than his own class (they had a baby).
     
    Last edited: Jun 18, 2008
  2. jcsd
  3. Jun 18, 2008 #2

    cristo

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    Staff Emeritus
    Science Advisor

    How did you calculate the speed? What is the difference between speed and velocity?

    What do you mean? A degree is a measure of angle.

    How did you get this? You need to show your working, or we can't help you.

    That looks fine to me.
    What do you think?
    Well.. that seems quite normal to me! You must have some notes from class, or some text that you are working from, to attempt these problems with.
     
  4. Jun 18, 2008 #3
    1) Speed = distance over time. So 45/3 = 15 km/s. Velocity is change in position. But I do not know where to go from there.

    2) I don't know how to draw it.

    3) It got cut off. It was in 7 seconds it is moving 4.7 m/s^2. Acceleration = velocity over time, so I did 4.7 = v/7, moved the 7 over and multiplied the two to get the answer.

    5) No clue :(
     
  5. Jun 18, 2008 #4
    3) u can start from origin on a graph. the scale on both axis should be same

    30 m north 80 degrees west --- draw a line of 30m at an angle of 80 degrees from y-axis towards west(left)

    3m north 10 degrees east ----from the end point of first line, draw a line of 3m at an angle of 10 degrees from y axis towards east(right)

    so on....
     
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