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Homework Help: Involves magnetic force and point charges with constant velocity.

  1. May 4, 2008 #1
    A point charge is moving at 1 x 10^6 meters per second. At the origin (0,0), a magnetic field of 1 T is applied into the page. The charge = 1.6 x 10^/10 C.

    1) Calculate the force.
    2) Calculate the exact location it hits the X intercept.
    3) Calculate the time is takes to hit the X intercept (starting from the origin).

    I can answer the first two questions. For the third, I calculated circumference and divided it by 2 to find the total distance traveled.

    My question is, if a magnetic force was created, was acceleration created as well?

    When I calculated the time, i first found the acceleration by using F = ma

    Once I found the acceleration, I plugged it into d = vt + 1/2 at2 to find the time.

    Should I have disregarded the centripital acceleration and just used d = vt?
  2. jcsd
  3. May 4, 2008 #2


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    Staff Emeritus
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    Gold Member

    Welcome to PF,

    Firstly it is important to realise that constant velocity is not the same as constant speed. In this case, the particle in travelling with constant speed (circular motion), but it's direction is constantly changing and is therefore accelerating, hence the velocity is not constant.

    What is the particle's initial position?
  4. May 4, 2008 #3
    Thanks so much for the reply. The initial position is (0,0). The question was worded "charge is moving initially at 1 x 10^6 m/s" I'm sorry I'm a little vague but this was a test question and I obviously don't have it in front of me.

    BTW, in order to calculate where it hit the x-axis, I used the formula r(radius) = mv/qb and multiplied by two.
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