at the sea side the sun shines equally on the sand and sea. assuming the both absorb the same amount of energy, why is the sand a lot hotter than the sea

Answer 1

The specific heat of water is much higher than the specific heat of the sand; therefore, q = mc*delta T. You can see for the same q and we will assume the same mass (although the mass of the sane probably is less than that of all of the sea water), the higher c causes delta T to be smaller.