The proton–proton cycle consumes four protons while producing 27 MeV of energy.
(a) At what rate must the Sun consume protons to produce its power output of 4x10²⁶ W?
(b) The present phase of the Sun’s life will end when it has consumed about 10% of its original protons. Estimate how long this phase will last, assuming the Sun’s 2x10³⁰ kg mass was initially 71% hydrogen.