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.