The hot surface of a circuit board is steadily dissipating heat at 8 w to the ambient air of 20 °c. the board itself is 15 cm wide and 20 cm long, and the heat loss on the other side of the board can be neglected. determine the average temperature of the hot surface when (a) the board is placed vertically (along 20-cm side), (b) the board is placed horizontally with the hot surface facing up, and (c) the board is placed horizontally with the hot surface facing down. assume the board surface has an emissivity of 0.8 and the surrounding surfaces are at 20 °c.

Boxing gloves are padded to lessen the force of a blow. (a) calculate the force exerted by a boxing glove on an opponent’s face, if the glove and face compress 7.50 cm during a blow in which the 7.00-kg arm and glove are brought to rest from an initial speed of 10.0 m/s. (b) calculate the force exerted by an identical blow in the gory old days when no gloves were used and the knuckles and face would compress only 2.00 cm. (c) discuss the magnitude of the force with glove on. does it seem high enough to cause damage even though it is lower than the force with no glove?

Based on the concept of the wave-like nature of light, huygens' theory of light postulates that the more light was "bent" by a substance the slower it would move while traversing across that substance. a) deflection b) interference c) refraction d) resonance

The items in the following list are all units of matter. which is the smallest unit that retains the properties of the matter? a.) atom b.) compound c.) electron d.) element