Elena makes a table to organize the functions of electric motor components. which functions belong in the cells marked x and y? component function brush x commutator y a. x: conducts current to the armature and reverses direction of current y: rotates as a result of changing magnetic forces b. x: rotates as a result of changing magnetic forces y: conducts current to the armature and reverses direction of current c. x: allows current to flow into the commutator y: conducts current to the armature and reverses direction of current d. x: allows current to flow into the commutator y: rotates as a result of changing magnetic forces

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.

Large electric fields in cell membranes cause ions to move through the cell wall. the field strength in a typical membrane is 1.0 x 10 7 n/c. what is the magnitude of the force on a calcium ion with charge +e? what is its acceleration? is it possible for a particle with the same charge as as calcium to have a different acceleration if placed at this location? what would change the acceleration: mass of the particle? diameter of the particle?

The ability to make things happen is also called a. heat b. force c. matter d. energy