Between 1930 and 2012what was the increase of the American farmer's ability to feed people without changing the amount of land used?

Heat is added to a piston-cylinder device filled with 2 kg of air to raise its temperature 400 c from an initial temperature of t1 27 cand pressure of pi 1 mpa. the process is isobaric process. find a)-the final pressure p2 b)-the heat transfer to the air.

Water at the rate of 1 kg/s is forced through a tube with a 2.5 cm inner diameter. the inlet water temperature is 15°c, and the outlet water temperature is 50°c. the tube wall temperature is 14°c higher than the local water temperature all along the length of the tube. what is the length of the tube?

Consider a beam traveling through diamond and impinging upon the diamond-air interface. the critical angle of incidence for total internal reflection to occur is closest to the following value: select one: a)-22.50° b)-23.85 c)-24.30 d)-23.40° e)-none of the above