Consider a packed bed of 75-mm-diameter aluminum spheres (rho = 2700 kg/m3 , c = 950 J/kg ⋅ K, k = 240 W/m ⋅ K) and a charging process for which gas enters the storage unit at a temperature of Tg, i = 300°C. If the initial temperature of the spheres is Ti = 25°C and the convection coeffcient is h = 75 W/m2 ⋅ K, how long does it take a sphere near the inlet of the system to accumulate 90% of the maximum possible thermal energy? What is the corresponding temperature at the center of the sphere? Is there any advantage to using copper instead of aluminum?

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia

the answer is c. the lower legs are levers, and the knees are fulcrums. the ankles hold the loads.