# Homework Help: Stick slip friction, spring force.

1. Mar 15, 2009

### MaxManus

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

The block has mass m. A spring (with spring constant k and equilibrium length b) is
attached to the block at the point x. The free end
of the spring is at the point xb. We move the free end of the spring with a constant
velocity u. The static and dynamic coefficients of friction for the contact between the
block and the bottom surface are μs and μd respectively. The acceleration of gravity
is g = 9.8m/s2.
The block starts at the position x(t0) = 0 at the time t0 = 0. The position xb of the
free end of the spring is xb(t0) = x(t0) + b at t0.

If the block starts at rest, what is the extension $$\Delta$$xc = ($$\Delta$$xb − $$\Delta$$x) of the spring when
the block starts moving?

Last edited: Mar 15, 2009
2. Mar 15, 2009

### tiny-tim

Hi MaxManus!

(is the spring vertical? )

Show us what you've tried, and where you're stuck, and then we'll know how to help!

3. Mar 15, 2009