Apoint charge, magnitude q, is at the origin of a coordinate system. a second charge q is brought to distance r from the charge from a very large distance away, then is taken in a semicircle around the charge so that it is opposite where it was but at the same distance, then brought out to distance 2r. what is the work done on the moving charge by the electric field of the first charge?
(a)
w=qq/(8 pi epsilon_0 r)
(b)
w = qq/(4 pi epsilon_0 r)
(c)
w = qq/(16 pi epsilon_0 r)
(d)
w=0

Ahair dryer is basically a duct in which a few layers of electric resistors are placed. a small fan pulls the air in and forces it through the resistors where it is heated. air enters a 1200 w hair dryer at 100 kpa and 22°c and leaves at 47°c. the cross-sectional area of the hair dryer at the exit is 60 cm2. neglecting the power consumed by the fan and the heat losses through the walls of the hair dryer, determine (a) the volume flow rate of air at the inlet and (b) the velocity of the air at the exit.