Homework Help Forum: Physics

Posted by for "bobpursley" on Friday, November 6, 2009 at 2:53pm.

If a 40 kg brick and a 400 kg brick each dropped from 1 m above a trampoline, find the lowest position of each brick. Assume the trampoline is a simple spring obeying Hooke's law with a k value of 12 000 N/m. So, I used mg(h+x)=1/2 k x^2 then solved for x in each case. and got 2 different values out of the quadratic formula: -0.223 m and -0.0000242 m given the question, how can I rule one of the answers out and choose the reasonable answer?

• Physics - bobpursley, Friday, November 6, 2009 at 3:02pm

  6000x^2-40kx- 40*9.8*1=0 where k is 1, or 10 x= (+40k+-sqrt(1600k^2+9.4E6)/12,000 for k=1 x= (40+-3067)/12000= 25cm ignore the -x, it has no physical meaning, the trampoline will not deform upward. for k=10 x= (+400+-sqrt(160000+9.4E6)/12000 x=(400+-3093)/12000=29cm check my math.

  
  

• Physics - Rachel, Friday, November 6, 2009 at 3:06pm

  you lost be. k= 12 000 N/m where are you getting 1 or 10

  
  

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