A drift current density of 120 A/cm2 is established in n-type silicon with an applied electric field of 18 V/cm. If the electron and hole mobilities are µn = 1250 cm2 /V–s and µp = 450 cm2 /V–s, respectively, determine the required doping concentration.

Asap and show ! a 14 kg rock starting from rest free falls through a distance of 5.0 m with no air resistance. find the momentum change of the rock caused by its fall and the resulting change in the magnitude of earths velocity. earth mass is 6.0 * 10^24 kg. show your work assuming the rock earth system is closed.

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

The great sandini is a 60.0-kg circus performer who is shot from a cannon (actually a spring gun). you don’t find many men of his caliber, so you him design a new gun. this new gun has a very large spring with a very small mass and a force constant of 1100 n/m that he will compress with a force of 4400 n. the inside of the gun barrel is coated with teflon, so the average friction force will be only 40.0 n during the 4.00 m he moves in the barrel. at what speed will he emerge from the end of the barrel, 2.50 m above his initial rest position?