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Dice Hanging from Mirroe

  • Thread starter bpw91284
  • Start date
67
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1. Homework Statement
A pair of fuzzy dice is hanging by a string from your rearview mirror. While you are accelerating from a stoplight to 29 m/s in
5.7 s, what angle θ does the string make with the vertical?

2. Homework Equations
v_f=v_0+a*t
x_f=x_0+v_0*t+0.5a*t^2
v_f^2=v_0^2+2*a(x_f-x_0)
x-x_0=[(v_0-v+v_f)/2]*2

And just sum of forces=0
F=ma

Note: v_f^2 is final velocity squared

3. The Attempt at a Solution
I'm lost because it seems to me that the mass of the dice must be known to solve?
 

Answers and Replies

144
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This is an accelerated frame of reference. You know the direction of the acceleration that the frame has. There is a fictious force and the natural force (gravity), what is the vectorial sum of these two?
 
312
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Forget about ficticious forces. Draw a picture and a free body diagram. First, solve for acceleration. The tension force acts at an angle, which means a component of tension accelerates the dice. If you do things correctly, mass should cancel out of the equation
 
103
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A good idea would be to draw a force diagram outside and inside of the car =). To get a frame of reference for which way the dice are accelerating.

They will be accelerating positively or negatively as the speed of the car =).

Also, split this up into two vectors x and y. Once you start to do all the calculations, you'll find that the mass cancels out in the end =).
 

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