Pulley with spring question -- Please help

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  • #1
nicky670
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Homework Statement:
In another set up where mass of block A is 𝑚𝐴 = 10.0 kg and the mass of block B is 𝑚𝐵 =12.0 𝑘𝑔. A spring with constant𝑘 = 90 𝑁 / 𝑚 is attached to block A as shown. The incline plane is 𝜃 = 37∘ and the coefficient of kinetic friction between the block A and theincline is 𝜇𝑘 = 0.30 as before. Block B is moving down and block A moving up the slope. (The magnitude of the spring force is
given by |𝐹𝑠𝑝| = 𝑘𝑥 where 𝑥 is the extension.)
Relevant Equations:
For Ma(perpendicular) = FN - Magcos(titre) = 0
Ma (Parallel) = Fsp + T - Ffriction - Magsin(titre) = Ma(a)

For Mb: Mbg - T = Mb(a)
Fsp = 90 x 0.12 = 10.8
Ffriction = Magcos(titre) x 0.30
I got the answer 2.09ms2 when the correct answer is 1.11ms2. What am i doing wrong here?

phy6.PNG
 
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Answers and Replies

  • #3
nicky670
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Isn't the spring force opposite to T?
But wouldn't the spring force push the block forward?
 
  • #4
haruspex
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But wouldn't the spring force push the block forward?
It says the spring has an extension of 0.12m.
 
  • #5
nicky670
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It says the spring has an extension of 0.12m.
When the spring extends, wouldn't it exert a force in the same direction as the tension force?
 
  • #6
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When the spring extends, wouldn't it exert a force in the same direction as the tension force?
When you stretch a spring, doesn't it pull back on you in the opposite direction?
 
  • #7
haruspex
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When the spring extends, wouldn't it exert a force in the same direction as the tension force?
Is an extended spring under tension or under compression?
 
  • #8
nicky670
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When you stretch a spring, doesn't it pull back on you in the opposite direction?
Oh, means to say when its extended it will have a tension pulling it back and if compressed there will be a force pushing the block forward?
 
  • #9
nicky670
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Is an extended spring under tension or under compression?
tension.
 
  • #10
haruspex
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Oh, means to say when its extended it will have a tension pulling it back and if compressed there will be a force pushing the block forward?
Yes.
 
  • #11
nicky670
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