Which best describes an element? a pure substance, a type of a mixture, a pure compound or an impure substance?

If two metal balls each have a charge of -10^-6 c and the repulsive force between them is 1 n, how far apart are they? (coulomb's constant is k = 9.0x 10^9 n-m^2/c^2? 9.5 m 9.0 mm 9.5 cm 0.9 m .

Na food processing facility, a spherical container of inner radius r1 5 40 cm, outer radius r2 5 41 cm, and ther- mal conductivity k 5 1.5 w/m · k is used to store hot water and to keep it at 100°c at all times. to accomplish this, the outer surface of the container is wrapped with a 800-w electric strip heater and then insulated. the temperature of the inner surface of the container is observed to be nearly 120°c at all times. as- suming 10 percent of the heat generated in the heater is lost through the insulation, (a) express the differential equation and the boundary conditions for steady one-dimensional heat conduction through the container, (b) obtain a relation for the variation of temperature in the container material by solving the differential equation, and (c) evaluate the outer surface tempera- ture of the container. also determine how much water at 100°c this tank can supply steadily if the cold water enters at 20°c.

Figure 9 on page 362 shows various motions of balls. the curved path followed by the yellow ball in b in picture b is result of a) inertia b) centripetal motion c) gravity and horizontal velocity d) linear motion