Trevor lifts a 10kg box to the top of a cliff which is 20m high, in half an hour, then drops the box over the cliff. How much power did he use to lift the box?

As part of an industrial process, air as an ideal gas at 10 bar, 400k expands at steady state through a valve to a pressure of 4 bar. the mass flow rate of air is 0.5 kg/s. the air then passes through a heat exchanger where it is cooled to a temperature of 295k with negligible change in pressure. the valve can be modeled as a throttling process, and kinetic and potential energy effects can be neglected. (a) for a control volume enclosing the valve and heat exchanger and enough of the local surroundings that the heat transfer occurs at the ambient temperature of 295 k, determine the rate of entropy production, in kw/k. (b) if the expansion valve were replaced by an adiabatic turbine operating isentropically, what would be the entropy production? compare the results of parts (a) and (b) and discuss.

You are standing on a boat. which of the following strategies will make the boat start moving? a. pushing the mast b. throwing some cargo out of the boat c. pushing the front ofthe boat d. pushing another passenger

Which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?