Anew cement mixing truck can be purchased for $100,000 and will have a salvage value of $50,000 at the end of 5 years. the cost of concrete mix for the truck is $100 per cubic yard. alternatively, the construction company can pay $105 per cubic yard to have concrete delivered by a third party. assume the construction company can order the concrete mix or delivery for the whole year on their account, and pay the full balance at the end of each year. at an interest rate of 10% per year, the minimum cubic yards of concrete that must be used each year to justify the purchase of a truck is closest to:

The temperature of air decreases as it is compressed by an adiabatic compressor. a)- true b)- false

Apump is used to circulate hot water in a home heating system. water enters the well-insulated pump operating at steady state at a rate of 0.42 gal/min. the inlet pressure and temperature are 14.7 lbf/in.2, and 180°f, respectively; at the exit the pressure is 60 lbf/in.2 the pump requires 1/15 hp of power input. water can be modeled as an incompressible substance with constant density of 60.58 lb/ft3 and constant specific heat of 1 btu/lb or. neglecting kinetic and potential energy effects, determine the temperature change, in °r, as the water flows through the pump.

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?