What is the energy equivalent of 5.0kg of mass?

Ah hah !  Sounds to me like an  " E = m c² "  question.

c = 3 x 10⁶  m/s

c² = 9 x 10¹² m²/s²

                       E  =  (5 kg)  x  (9 x 10¹² m²/s²)

                           =       45 x 10¹²  kg-m²/s²

                           =       4.5 x 10¹³  newton-m

                           =        4.5 x 10¹³ Joules  . 

That's the energy needed to

-- run a 1000-watt blow-dryer for roughly  1,427 years .
or
-- run a 400-horsepower truck, wide open, pedal to the metal,
   for   4.78 years . 

Answer: buoyancy forceexplanation: in simple terms, the principle states that the buoyancy force on an object is equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational acceleration, g. this is also known as upthrust.