One of the stable isotopes of lithium has 3 protons and 4 neutrons, so its atomic mass is 7. Assume that a lithium atom initially at rest radiates a photon of energy 1.8488 eV and recoils.

How long does it take for the recoiling atom to travel 1 mm? Assume that the lithium atom travels in a straight line without any collisions.
Note: 1 amu = 1.66 x10^-27 kg

Be careful with the units!

t = s