Can we boil water by dropping it off a cliff? For 1 kg of liquid water at room t

Question

Can we boil water by dropping it off a cliff?

For 1 kg of liquid water at room temperature (25 oC) determine the change in internal energy associated with an increase of the temperature 1o C to 26 oC. What would be the necessary change in elevation of 1 kg of liquid water at room temperature (25 oC) needed to increase the energy of the system this same amount by changing the potential energy? If the energy of the system were to be changed this same amount by changing the kinetic energy, to what speed must the system be accelerated if it is initially at rest? Using these results, comment on the likely reasonableness of neglecting changes in KE and PE for thermodynamic problems involving liquid water and changes in temperature.

Explanation / Answer

change = 1000*4.2* 25 = 105,000 J

mgh = 105,000

so h = 105,000 / ( 9.8 * 1 ) = 10,714.286 metres

for speed

0.5 * 1kg * v^2 = 105,000

so sped = 458.25757 m/sec

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