At the foot of a waterfall, the water’s temperature is higher than it is at the top. As the water falls, its gravitational potential energy at the top is converted into thermal energy at the bottom. The specific heat capacity of water is $4200\,\text{J kg}^{-1}\,^\circ\text{C}^{-1}$. What is the temperature difference for a waterfall of height $21\,\text{m}$?
- A$0.005\,^\circ\text{C}$
- B$0.05\,^\circ\text{C}$
- C$20\,^\circ\text{C}$
- D$200\,^\circ\text{C}$