me 3333 thermo fall-10 hw-iv problems
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ME 3333 Thermodynamics
HW‐IV_Problems_Fall 2010
2‐32E The force F required to compress a spring a distance x is given by F – F0 = kx where k is the spring constant and F0 is the preload. Determine the work required to compress a spring whose spring constant is k = 200 lbf/in a distance of one inch starting from the free length where F0 = 0 lbf. Express your answer in both lbf ∙ ft and Btu. Answer: 8.33 lbf ∙ ft ; 0.0107 Btu
2‐38 Determine the power required for a 1150‐kg car to climb a 100‐m‐long uphill road with a slope of 30o (from horizontal) in 12 s (a) at a constant velocity, (b) from rest to a final velocity of 30 m/s, and (c) from 35 m/s to a final velocity of 5 m/s. Disregard friction, air drag, and rolling resistance. Answer: (a) 47.0 kW, (b) 90.1 kW, (c) ‐10.5 kW
2‐51 A fan is to accelerate quiescent air to a velocity of 8 m/s at a rate of 9 m3/s. Determine the minimum power that must be supplied to the fan. Take the density of air to be 1.18 kg/m3.Answer: 340 W
2‐76 An oil pump is drawing 35 kW of electric power while pumping oil with ρ = 860 kg/m3 at a rate of 0.1 m3/s. The inlet and outlet diameters of the pipe are 8 cm and 12 cm, respectively. If the pressure rise of oil in the pump is measured to be 400 kPa and the motor efficiency is 90 percent, determine the mechanical efficiency of the pump. Answer: 83.6%
2‐83C What is the greenhouse effect? How does the excess CO2 gas in the atmosphere cause the greenhouse effect? What are the potential long‐term consequences of greenhouse effect? How can we combat this problem?
1500 kg