Using the conservation of energy find speed

  • #1
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Homework Statement


A spring, having a force constant of 6.0x102 N/m, is held in a vertical position and compressed 0.30m. A 5.0 kg mass is then placed on top of the spring. THe mass is then releases. Neglecting air resistance and the mass of the spring

The Attempt at a Solution



Ek1 = Ek2
1/2kx^2 = 1/2kx^2 + 1/2mv^2
1/2(600N/m)(0.3m)^2 = 1/2(600N/m)(0.2m)^2 + 1/2(5 kg)v^2
27 J - 12 J = (2.5 kg)v^2
2.45 m/s=V

Im confused if we need to add any sort of gravitational potential energy to the ball?
 

Answers and Replies

  • #2
PhanthomJay
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Homework Statement


A spring, having a force constant of 6.0x102 N/m, is held in a vertical position and compressed 0.30m. A 5.0 kg mass is then placed on top of the spring. THe mass is then releases. Neglecting air resistance and the mass of the spring

The Attempt at a Solution



Ek1 = Ek2
1/2kx^2 = 1/2kx^2 + 1/2mv^2
1/2(600N/m)(0.3m)^2 = 1/2(600N/m)(0.2m)^2 + 1/2(5 kg)v^2
27 J - 12 J = (2.5 kg)v^2
2.45 m/s=V

Im confused if we need to add any sort of gravitational potential energy to the ball?
You need to consider both gravitational and spring potential energies and kinetic energy. Are you trying to determine the speed when the mass leaves the spring?
 
  • #3
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You need to consider both gravitational and spring potential energies and kinetic energy. Are you trying to determine the speed when the mass leaves the spring?

yes, the velocity when it has moved up 0.20 m from the compressed position on the spring.
 
  • #4
PhanthomJay
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When it moves up 0.2 m, the spring is now compressed by how much? Don't forget the gravitational PE.
 
  • #5
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When it moves up 0.2 m, the spring is now compressed by how much? Don't forget the gravitational PE.

umm.... 0.1?
 
  • #6
PhanthomJay
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Yes.
 
  • #7
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Yes.

so
Ek1 = Ek2
1/2kx^2 = 1/2kx^2 + 1/2mv^2
1/2(600N/m)(0.3m)^2 = 1/2(600N/m)(0.1m)^2 + 1/2(5 kg)v^2
27 J - 3 J = (2.5 kg)v^2
3.098 m/s=V
 
  • #8
PhanthomJay
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What happened to the gravitational potential energy term you were inquiring about??
 
  • #9
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What happened to the gravitational potential energy term you were inquiring about??

umm what do you mean?
 
  • #10
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What happened to the gravitational potential energy term you were inquiring about??

Ek1 = Ek2
1/2kx^2 = 1/2kx^2 + 1/2mv^2
1/2(600N/m)(0.3m)^2 = 1/2(600N/m)(0.2m)^2 + 1/2(5 kg)v^2 + (5 kg)(9.8 m/s^2)(0.2 m)
27 J - 3 J - 9.8 J= (2.5 kg)v^2
2.38 m/s=V
 
  • #11
PhanthomJay
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Looks good now!
 
  • #13
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Tell me who u are, u go to my school. DONT IGNORE ME
 
  • #14
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Tell me who u are, u go to my school. DONT IGNORE ME

? who r u?
 

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