In order to keep an object weighing 40 Newtons moving at constant speed along a horizontal surface, a force of 15 Newtons is required. The force of friction between the surface and the object is

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.

He acceleration due to gravity on the surface of mars is about one third the acceleration due to gravity on earth’s surface. the weight of a space probe on the surface of mars is about

If it takes 200 joules of energy to lift a bucket of water 3 meters in 2 seconds, how much power would be required to do the same amount of work in 5 seconds?