Using the conservation of energy find speed

Lolagoeslala

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?

Homework Helper
Gold Member

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?

Lolagoeslala
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.

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

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

umm... 0.1?

Homework Helper
Gold Member
Yes.

Lolagoeslala
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

Homework Helper
Gold Member
What happened to the gravitational potential energy term you were inquiring about??

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

umm what do you mean?

Lolagoeslala
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

Homework Helper
Gold Member
Looks good now!

Lolagoeslala
looks good now!

thanks :d

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

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

? who r u?