Spring constant and conservation of energy

[Knfoster]

Homework Statement

The ball launcher in a pinbgall machine has a spring that has a force constant of 36 N/cm. THe surface on which the ball moves is inclined theta=10.1 degrees with respect to the horizontal. If the spring is initially conressed 4.25 cm, find the launching speed of a .120 kg bawhen the plunger is released. Friction and the mass of the plunger e negligible.

Homework Equations

PE=.5k(xf-xi)^2
KE=.5mv^2

The Attempt at a Solution

I'not sure what launching speed is supposed to be, it supposed to be an answer that doesn't require units. Does that mean I need to be finding the spring constant? If so, do I just set the KE=PE?

 

[LowlyPion]

They give you the spring constant. 36 N/cm.

So think conservation of energy.

Spring potential depressed = kinetic energy at release point plus additional increase in gravitational potential energy at release point .

 

[Feldoh]

The force constant is the spring constant. You're looking for a velocity.

Think about it if we compress a spring at some angle we are storing potential energy in the spring, but we also have to take into account gravity, does this help?

 

[Knfoster]

It can't be simply velocity that I'm looking for because an answer not requiring units is needed. Any other ideas?

 

[Feldoh]

I'm pretty sure it's got units -- it asks for the launching speed. Speed's have units of distance per time.

 

[Knfoster]

I know... it should but, I'm doing homework through lon-capa and it's telling me that it doens't require units, so it can't be asking for velocity.

 

[LowlyPion]

They ask for speed.

Calculate it as m/s.

Ignore their not asking for units.