Mechanical Engineering Answers

1.)A 20lbm object is located 300 ft above the ground. What is the potential energy of the object in lbf-ft, BTU, and cal?

2.)A mole of a certain ideal gas was inside a container. The gas has a temperature of 70°F and a pressure of 20 psi. Find the volume of the gas in m^3.

An inventor claims to have developed a heat

engine that receives 700 kJ of heat from a source

at 500 K and produces 300 kJ of net work while

rejecting the waste heat to a sink at 290 K. Is this

a reasonable claim? Why?

Find the values of Cp and ᵞ for a gas whose gas

constant is 0.324 kJ/kg K and Cv = 0 84 kJ/kg K.

If 2.25 kg of this gas with an initial volume of

1.15 m3 undergoes a process during which its

pressure remains constant at 7 bar and its

temperature becomes 280‘C at the end of the

process, calculate: (a) the change in internal

energy, (b) the change in enthalpy, (c) the

transferred heat, and (d) the work done.

A synthetic belt of density 994kg/m³ is used in an open-belt drive. The belt is wrapped around a pulley of diameter 900mm running at 324rpm. If the angle of contact with the small pulley is 2∙π/3 radians and the maximum stress on the tight side is limited to 2000kPa. The coefficient of friction between the belt and the pulley is 0.35 and the belt width and thickness are 250mm and 10mm, respectively.  . Calculate:

 The power transmitted by the belt in Watts (W)

An R-410a heat pump cycle shown in the figure below has an R-410a flow rate of 0.05 kg/s with 5 kW into the compressor. The following data are given:

State 1 2 3 4 5 6

P, kPa 3100 3050 3000 420 400 390

T, oC 120 110 45 -10 -5

h, kJ/kg 377 367 134 280 284

Calculate the heat transfer

a) from the compressor

b) from the R-410a in the condenser

c) to the R-410a in the evaporator

Consider an ordinary shower where hot water at 60 oC is mixed with cold water at 10 oC. If it is desired that a steady stream of water at 45 oC be supplied, determine the ratio of the mass flow rates of the hot to cold water. Assume the heat losses from the mixing chamber to be negligible and the mixing to take place at a pressure of 150 kPa.

A Certain rocket, initially at rest, is shot straight up with an acceleration of 6t m/s2 during the first seconds after blast-off, after which the engine cuts out and is subject

only to gravitational acceleration. How high will the rocket go? Use g=10 m/s2

A solid cylinder, 0 ≤ r ≤ b, is initially at zero temperature. For times t > 0, the boundary condition at r = b is subjected to a time-dependent prescribed temperature f (t) defined by

First plot (i.e., sketch) the boundary condition f (t). Using Duhamel’s theorem, develop an expression for the temperature distribution T(r,t) in the cylinder for times (i) τ₁ 3.

Steam at 3.5 MPa and with a 75.38C superheat rejects 1973.36 kJ per kg of steam heat at a

constant pressure, determine

a. Properties of steam at state 1

b. Properties of steam at state 2

c. Final Temperature

d. Change in specific entropy

A piston-cylinder device initially contains 10L of liquid water at 25C and at atmospheric

pressure of 101.325 kPa. Heat is added at constant pressure until the entire liquid is

vaporized. (a) what is the mass of water (b) final temperature (c) amount of heat absorbed

by the water.