2.30 Suppose that the radius of a typical cell is 10 mm and that inside it 106 ATP molecules are hydrolyzed each second. What is the power density of the cell in watts per cubic meter (1 W = 1 J s−1)? A computer battery delivers about 15 W and has a volume of 100 cm3. Which has the greater power density, the cell or the battery?

Answer and Explanation: One ATP release approximately 30.5kJ/mol of energy. Using Avogadro's constant, it is known one mol corresponds to molecules, so 106 ATP molecules releases:

E =

E = J

A cell is approximately a sphere. Volume of a sphere is given by

V =

Changing radius from mm to m:

r = m

Then, volume is

V =

V = m³

Power density is given by

power = 12.8. W/m³

Power density for a the cell is 12.8. W/m³.

Power density for battery is

100 cm³ = m³

power =

power = W/m³

Comparing cell and battery, battery has a greater power density.

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force