Living cells "pump" singly ionized sodium ions, Na+, from the inside of the cell to the outside to maintain a membrane potential Δ V membrane = V in − V out = − 70 mV . It is called pumping because work must be done to move a positive ion from the negative inside of the cell to the positive outside, and it must go on continuously because sodium ions "leak" back through the cell wall by diffusion. How much work must be done to move one sodium ion from inside to the outside of the cell?

Two thin 80.0- cm rods are oriented at right angles to each other. each rod has one end at the origin of the coordinates, and one of them extends along the x- axis while the other extends along the yaxis. the rod along the x- axis carries a charge of - 15.0 μ c distributed uniformly along its length, and the other rod carries 15.0 μ c uniformly over its length. find the magnitude and direction of the net electrical force that these two rods exert on an electron located at the point (40.0 cm, 40.0 cm). (e

The least penetrating form of radiation is

The two stars in a certain binary star system move in circular orbits. the first star, alpha, has an orbital speed of 36 km/s. the second star, beta, has an orbital speed of 12 km/s. the orbital period is 137 d. a) what is the mass of the star alpha? b) what is the mass of the star beta?