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Physics Problems ? (particle acceleration)

  1. Jan 29, 2009 #1
    Physics Problems ??? (particle acceleration)

    I'm working on my last 2 of 30 or so physic problems and am pretty lost on what to do/how to even start. The homework is due in exactly 3 hrs, I already have an "A" on this assignment but would like to squeeze on these last 6 points or so.

    Question 6

    A particle experiences a constant acceleration that is north at 100 m/s2. At t = 0, its velocity vector is 45 m/s east. At what time will the magnitude of the velocity be 100 m/s?

    Question 7

    An accelerometer-a device to measure acceleration-can be as simple as a small pendulum. Suppose you are flying a small plane in a straight horizontal line and your accelerometer hangs 11° behind the vertical, opposite the direction of motion. What is your acceleration?
  2. jcsd
  3. Jan 29, 2009 #2


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    Re: Physics Problems ??? (particle acceleration)

    What are your thoughts so far?


    Qu #6: You're given the component of velocity in the east direction and the magnitude of the velocity at a certain time, how can you work out the north component?

    Qu #7: Draw a free body diagram of the pendulum and see if you can work from there.
  4. Jan 29, 2009 #3
    Re: Physics Problems ??? (particle acceleration)

    Question 6 I don't really understand what they are trying to get across.

    So a particle is going N at 100 ms^2

    So that gives me acceleration is=100 constantly

    It gives me east velocity at 45 m/s at t=0 (time)

    I'm assuming the North part is important, but I dont know what equation they're looking for or what in general I'm suppose to find.:uhh:

    As far as question 7 goes, am I suppose to use gravity (9.8 m/s2) for anything. The plane is obviously accelerating because the pendulum is back 11 degrees. Just like when a car accelerates, your pushed into the seat.

    I was thinking of accelerating formulas I know, and a=v/t doesn't work. I dont have velocity or time. The only component that I feel I have would be the angle which is 11 degrees. Which I don't know what I'm suppose to use that for.
  5. Jan 29, 2009 #4
    Re: Physics Problems ??? (particle acceleration)

    I guess there were a lot of students confused on question 7 so this is what are instructor said.

    HW problems from Chapter 3 Hint for Problem 7: The tension on the pendulum string has an x and y component, the y component is T cos theta and is equal to mg - use this to solve for T. The x component is balanced by the forward acceleration of the airplane - so use T sin theta - a*m to find a.

    I'm going to see if I can figure it out now.
  6. Jan 29, 2009 #5


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    Re: Physics Problems ??? (particle acceleration)

    Stick with 6 for now. What do you know about vectors, their components and their magnitudes? That is all you really need to solve this question. The following page may also help.

  7. Jan 29, 2009 #6


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    Re: Physics Problems ??? (particle acceleration)

    Acceleration vectors can be added together using the same math as you've been using to add velocity vectors. You do not need to really break the components up into x-y, because you already know the direction of the acceleration!!

    1. Due to gravity directly down (-y).
    2. Due to the plane directly to the back (-x).
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