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Homework Help: Fuzzy dice problem help please

  1. Sep 19, 2008 #1
    1. The problem statement, all variables and given/known data
    A pair of fuzzy dice is hanging by a string from your rearview mirror. while you are accelerating from a stoplight to 28 m/s in 6.0 s, what angle does the string make with the verticle?

    2. Relevant equations
    im having trouble finding the mass and the force on the dice i know you are suppose to use F=Mg but like i said i have to find the force of the die and to do that i have to find the mass

    3. The attempt at a solution

    knowns unknown i used this equation to get the mass but im unsure about it
    V= 28 m/s angle y=yo+Vyot-1/2gt^2
    T=6.0 mass
    g=9.8m/s force
  2. jcsd
  3. Sep 19, 2008 #2


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    Don't you also know that V = a*T ?

    And if you know the horizontal acceleration won't that affect the hanging dice according to vector addition with gravitational acceleration? Hence won't you be able to calculate the angle? All without any consideration of what the mass may be.
  4. Sep 19, 2008 #3
    i don't understand how there is a horizontal acceleration because its hanging so i thought it was a vertical and since its vertical i thought the acceleration would be 9.8 m/s im just really unsure im confused now
  5. Sep 19, 2008 #4


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    Both accelerations are affecting the dice.

    One horizontal. One vertical. Added together they yield a resultant force.

    But since they are acting from different directions they must be added as you would add two vectors. One is 9.8 and the other what you calculate for the car's acceleration.

    When you add them in this manner you get an angle as well as a magnitude. The question is only asking you for the angle.
  6. Sep 19, 2008 #5
    but don't you have to find the mass of the die so you can calcutlate the force exerted on the die?
  7. Sep 19, 2008 #6


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    If you want to deal with it as Forces, then that's fine too. But F = ma and whether you figure the force vectors or the acceleration vectors the mass is a constant that merely relates the acceleration to force as a scalar. But it's the relationship between the two vectors that determines the angle.

    If you prefer then do the equations and carry the mass as unknown. When you calculate your angle see if you need to know the mass.
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