A 15cm x 20cm printed circuit board is to be cooled by natural convection at room temperature of 20oC. The PCB is dissipating heat at 8W f power in steady operation, determine average temperature of the hot surface of the board when (a) the board is vertical, (b) horizontal with hot surface facing up, and (c) horizontal with hot surface facing down. Emissivity of the board surface is 0.8/

Two resistors r1 and r2 may be connected either in series or parallel across an ideal battery with emf ε. we desire the rate of energy dissipation of the parallel combination to be 8.75 times that of the series combination. if r1 = 105 ω, what are the (a) smaller and (b) larger of the two values of r2 that result in that dissipation rate?

Can you receive a shock severe enough to prevent you from releasing the wire from an ordinary outlet with dry hands? a. no b. yes explain

Review multiple-concept example 7 in this chapter as an aid in solving this problem. in a fast-pitch softball game the pitcher is impressive to watch, as she delivers a pitch by rapidly whirling her arm around so that the ball in her hand moves in a circle. in one instance, the radius of the circle is 0.626 m. at one point on this circle, the ball has an angular acceleration of 66.1 rad/s2 and an angular speed of 12.6 rad/s. (a) find the magnitude of the total acceleration (centripetal plus tangential) of the ball. (b) determine the angle of the total acceleration relative to the radial direction.