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Homework Help: Forces on a ball in a moving car

  1. Oct 20, 2008 #1
    1. The problem statement, all variables and given/known data

    a) A 1 kg ball hands from a 1m rope in a car accelerating at 5 m/s^2, Does the ball have an acceleration?if so what are the magnitude and direction of the balls acceleration

    b) suppose the ball makes a 10 degree angle witht he vertical. If possible determine the truck's velocity, if possible determine the truck's acceleration.

    2. Relevant equations

    F=ma? lol

    3. The attempt at a solution

    a) Ok so i assume the ball would have an acceleration but how do i fugre it out? I know gravity acts on it and the tension of the rope acts on it...and i assume if the car is accelerating then the ball will swing backwards and settle in a position where the rope is slanting towards the back side of the car... but how do i actually calculate them? do i break down the forces in the x and y components? would then the y component be gravity straight down or gravity along the angle at which the rope is bent or what?

    b) Well i know we cant determine velocity at least, but we should be able to determine the acceleration...but how?

    if it makes a 10 degree angle to the vertical...then the force of tension on the rope would be t = mg / cos(10 degrees) (is this right)? I really have no idea how to do either part, can i get a hint of where to start
  2. jcsd
  3. Oct 20, 2008 #2


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    Staff Emeritus
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    Homework Helper

    (a) What is the ball's motion relative to the car?

    (Hint: the answer is simpler than you might think.)
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