**P. 4106.** A biro (ballpoint pen), which contains a spring, is pressed against a support at the bottom of an inclined plane as shown *in the figure,* and then suddenly it is released. The table below shows our measured data, the distance covered by the ballpoint pen as a function of the angle of inclination of the plane :

Using this table determine the initial speed of the biro and the coefficient of kinetic friction between the plane and the biro.

(4 points)

**P. 4110.** The horizontal part of the U-shaped tube shown *in the figure* is 10 cm, and its vertical branches are long enough. The cross section of the tube is 1 cm^{2}. First, 20 cm^{3} water is poured into the tube, then 20 cm^{3} oil is poured into the left branch. , . The whole system is accelerated towards the left, at an acceleration of *a*. Determine and graph the difference between the level of water and the level of oil as a function of the acceleration.

(5 points)