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Force problem help!

  • Thread starter Flaming Toilet
  • Start date

Flaming Toilet

Here's the question: A pair of fuzzy dice is hanging by a string from your rearview mirror. While you are acclerating from a stoplight to 20.0 m/s (in 5.0 sec.), what angle theta does the string make with the vertical?

Ok, I drew a force diagram with F (tension; upward direction)on the string and mg (weight) going down. Then, I found acceleration using the Vf-Vi divided by time : a=(Vf-Vi)/t
a=(20.0 m/s - 0 m/s)/5.0 s
a= 4.0 m/s squared

However, I have no idea what to do next. Can anyone give a hint(s) on what to do next?
 

Claude Bile

Science Advisor
1,471
19
Think in terms of components.

Since there is no vertical motion of the fluffy dice, the vertical component of the tension must equal the weight of the dice.

There horizontal acceleration which you calculated must also be supplied by the tension in the string.

Since you know the two components of force supplied by the tension in the string, you can work out which direction the tension (and hence the string) must be pointing in.

Claude.
 

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