We want to find how much charge is on the electrons in a nickel coin. follow this method. a nickel coin has a mass of about 5.7 g.
a. find the number of atoms in a nickel coin. each mole (6.02 × 10^23 atoms) has a mass of about 57.9 g. answer in units of atoms.
b. find the number of electrons in the coin. each nickel atom has 28 electrons/atom. answer in units of electrons.
c. find the magnitude of the charge of all these electrons. answer in units of c.

this means that the temperature of both substances will be equal

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me