A girl on a skateboard (total mass of 40 kg) is moving at a speed of 10 m/s at the bottom of a long road. The road is inclined at 20o with respect to the horizontal. If she travels 14.2 m upward along the road before stopping, without pushing in any way, what is the net frictional force on her?

Students in an introductory physics lab are performing an experiment with a parallel-plate capacitor made of two circular aluminum plates, each 11 cm in diameter, separated by 1.0 cm. how much charge can be added to each of the plates before a spark jumps between the two plates? for such flat electrodes, assume that value of 3×106n/c of the field causes a spark.