One mole of helium atoms has a mass of 4 grams. if a helium atom in a balloon has a kinetic energy of 2.176 × 10^-21j, what is the speed of the helium atom? (the speed is much lower than the speed of light.)

Aphoton is absorbed by an electron that is in the n = 3 state of a hydrogen atom, causing the hydrogen atom to become ionized. very far away from the nucleus, the released electron has a velocity of 750,000 m/s. what was the wavelength of the absorbed photon?