A ball is thrown into the air with 100 J of kinetic energy, which is transformed to gravitational potential energy
at the top of its trajectory. If it returns to its original level less than 100 J of kinetic energy, the ball
encountered
a. air resistance.
b. gravitational acceleration.
c. a faster descent time.
d. a decrease of its mass.

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.

In a system, when potential energy decreases, then entropy also decreases. true false

What is the temperature in degrees celsius of a substance with a tempature of 49k