This problem will be compared to the problem of natural convection from the ground. a team of soil scientists are interested in finding out how much grasses contribute to heat transfer from the earth surface to the ambient air, thereby cooling down the surface temperature. they model that the grass blades act as fins. the ground temperature is 33 c, while the air above is 22 c. we estimate that the heat transfer coefficient h-1.0 w/m2-c (not the value in the other problem). the ground is horizontal and flat, of size 20 m by 20 m surrounded by a fence. the grass is 8.0 cm long, and we will apprpximate that each blade has a rectangular cross section 0.1 mm 1.0 mm, of uniform cross section. an approximate value of the conductivity k is 40% of water, or 0.24 w/m-c. there are about 50 blades of grass per cm2- 500.000/m2- 200 million on the whole plot of ground. what is the heat loss from the ground due to the grass acting as fins? .
a)-74 w b)-15,000 w c)-2,200 w d)-0.0322 e)-610w

Which law represents the thermodynamic statement of the conservation of energy of a system? a. the fourth law b. the first law c. the second law d. the third law

Very large accelerations can injure the body, especially if they last for a considerable length of time. one model used to gauge the likelihood of injury is the severity index ( ), defined as =/ . in the expression, is the duration of the accleration, but is not equal to the acceleration. rather, is a dimensionless constant that = the number of multiples of that the acceleration is equal to. in one set of studies of rear-end collisions, a person's velocity increases by 13.7 km/h with an acceleration of 36.0 m/s2 . let the + direction point in the direction the car is traveling. what is the severity index for the collision?

In the future, people will only enjoy one sport: electrodisc. in this sport, you gain points when you cause metallic discs hovering on a field to exchange charge. you are an electrodisc player playing the popular four disc variant. the disks have charges of qa = −8.0 µc, qb = −2.0 µc, qc = +5.0 µc, and qd = +12.0 µc. (1) you bring two disks together and then separate them. you measure the resulting charge of these two disks and find that it is +5.0 µc per disk. which two disks did you bring together? (a) a and b (b) a and c (c)a and d (d)b and c(e) b and d (f) c and d. (2) you bring three disks together and then separate them. you measure the resulting charge of these three disks and find that it is +3.0 µc per disk. which three disks did you bring together? a, b, and c (a) a, b, and d (c) a, c, and d (d) b, c, and d. (3) given the resulting charge of each disk measured in (b) is +3.0 µc, how many electrons would you need to add to a disk of this charge to electrically neutralize it? electrons