Homework Help: Kinetics, springs

1. Mar 22, 2010

red123

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

The 2-lb collar C fits loosely on the smooth shaft. If the spring is unstretched when s = 0 and the collar is given a velocity of 15 ft/s, determine the velocity of the collar when s = 1 ft.

2. Relevant equations

F = kx

3. The attempt at a solution

x = l-l0 = (√[1 + s2] - 1) ft

Fsp = kx = [4√(1 + s2) - 4] lb

So, now I've found the spring force, how does velocity fit into this?

Last edited: Mar 22, 2010
2. Mar 22, 2010

Kabbotta

Kinetic energy. Some has been given to the spring, whatever is left...

3. Mar 22, 2010

red123

But how do I calculate the velocity?

4. Mar 23, 2010

Kabbotta

I guess I am a little surprised they gave you a question this hard without even explaining how to calculate kinetic energy.

Work-Kinetic Energy Thm.
$$K = 1/2mv^2$$
$$\sum W = K_{f} - K_{i} + W_{other forces}$$

The spring force is your other force doing work, and it will be negative work that takes away some kinetic energy, the final kinetic energy contains the velocity you are looking for, but the spring force is not constant so you have to do an integral for the work.

$$W_{spring} = \int F \cdot dx$$