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 [tex]\Delta[/tex]xc = ([tex]\Delta[/tex]xb − [tex]\Delta[/tex]x) of the spring when the block starts moving?