Using the conservation of energy find speed

1. Nov 10, 2012

Lolagoeslala

1. The problem statement, all variables and given/known data
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

3. 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?

2. Nov 10, 2012

PhanthomJay

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. Nov 10, 2012

Lolagoeslala

yes, the velocity when it has moved up 0.20 m from the compressed position on the spring.

4. Nov 10, 2012

PhanthomJay

When it moves up 0.2 m, the spring is now compressed by how much? Don't forget the gravitational PE.

5. Nov 10, 2012

Lolagoeslala

umm.... 0.1?

6. Nov 10, 2012

PhanthomJay

Yes.

7. Nov 10, 2012

Lolagoeslala

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. Nov 10, 2012

PhanthomJay

What happened to the gravitational potential energy term you were inquiring about??

9. Nov 10, 2012

Lolagoeslala

umm what do you mean?

10. Nov 10, 2012

Lolagoeslala

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. Nov 10, 2012

PhanthomJay

Looks good now!

12. Nov 10, 2012

Lolagoeslala

thanks :d

13. Nov 12, 2012

Tupac

Tell me who u are, u go to my school. DONT IGNORE ME

14. Nov 12, 2012

? who r u?