Tensile force in elevator problem

  • Thread starter bdh2991
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  • #1
bdh2991
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Homework Statement


Two blocks, each of mass m are hung from the ceiling of an elevator as in the figure below. The elevator has an upward acceleration a. The strings have negligible mass.

http://imageshack.us/a/img856/2241/5p031.gif [Broken]

Find the tensions T1 and T2 in terms of m, a, and g.

Which string would break first if a was sufficient large?

What are the tensions if the cable supporting the elevator breaks?



Homework Equations



F = ma

The Attempt at a Solution



My answers were:

T1 = 2(ma + mg)
T2 = ma + mg

the upper string would break first

T1 = 2(-ma + mg)
T2 = -ma + mg

can anyone please check my work and see if these answers are correct? thanks
 
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Answers and Replies

  • #2
PhanthomJay
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Looks good for the first part. For the second part, the elevator could no longer be accelerating up, since only gravity firce would be acting down. The elevator and its contents would be in free fall. In free fall, what is the acceleration? Redo your calcs for the tensions.
 
  • #3
bdh2991
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Looks good for the first part. For the second part, the elevator could no longer be accelerating up, since only gravity firce would be acting down. The elevator and its contents would be in free fall. In free fall, what is the acceleration? Redo your calcs for the tensions.

So...if the object is in free fall that would mean:

T1 = 0 and T2 = 0???
 
  • #4
PhanthomJay
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Yes, good.
 
  • #5
bdh2991
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Thank you for the help. Makes sense now that i think about it the right way
 

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