Arod of diameter d=25mm and thermal conductivity k=60w/(m*k) protrudes normally from a furnace wall that is at tw=200°c and is covered by insulation of thickness lins=200mm. the rod is welded to the furnace wall and is used as a hanger to support instrumentation cables. to avoid damaging the cables, the temperature of the rod at its exposed surface, to, must be maintained below a specified operating limit of tmax=100°c. the ambient air temperature is 30°c, and the convection coefficient is 17.0 w/(m2*k). a) derive an expression for the exposed surface

Using a wheel and axle, a farmer is trying to lift a bucket of water from the bottom of a well. the larger wheel has a radius of 40 cm compared to the axle that has a radius of 10 cm. if a bucket of water is 50 n, then how much effort is required to raise it? 12.5 n 200 n 2 n 500 n

Which car has the most kinetic energy? a. a car of mass 1000 kg with a speed of 3 m/s b. a car of mass 2000 kg with speed 7 m/s c. a car of mass 1000 kg with speed 7 m/s d. a car of mass 2000 kg with speed 3 m/s

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?