A light spring with a force constant of 12 is connected to a wall and to a 1.9 toy bulldozer, as shown in the figure.(Figure 1) When the electric motor in the bulldozer is turned on, it stretches the spring for a distance of 0.45 before its tread begins to slip on the floor.
1) Which coefficient of friction (static or kinetic) can be determined from this information and why?
2) What is the numerical value of this coefficient of friction?