Engineering Answers

A perfect gas having c_P = 1017.4 J/kg-K and m = 28.97 flows adiabatically in a converging passage with a mass flow rate m = 29.188 kg/s. At a particular cross section, M = 0.6, T = 550 K, and P = 2.0 middot 10^5 N/m^2. Calculate the area of the cross-section of the passage at that point.

Define these four acronyms and explain how they affect the transportation planning process: MPO, CLRP, TIP, and STIP. Describe the composition of one of them.

(Applications of Maxima and Minima Using an Auxiliary Variable)

A man on an island 12 mi. south of a straight beach wishes to reach a point on shore 29 mi. east. If a motorboat, making 20 mi. per hr., can be hired at the rate of $2.00 per hr. for the time it is actually used, and the cost of land transportation is $0.06 per mi., how much must he pay for the trip.

Get all the loads on all members including the supports. Using method of joints.

Length of truss - 30meters

Height of king truss - 4meters

Distances of every queen posts - 3meters

Support - roller at right and pinned at left part

Loadings - downward loading in every queen post is 18KN

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1.1 Medupi power station uses coal of calorific value of 5880 kcal/kg to generate electricity. They use 14.3 tonnes of coal every 25 minutes to generate the maximum demand of the power station. The thermal and electrical efficiency of the power station are 24.2% and 81.1%, respectively. The cost of purchasing the coal is R800 per tonne.

1. Determine the overall efficiency of the power station (%). 

Find the compound amount at the end of 3 years if P2000 is invested at 8% compounded semi - annually.

A 20 kVA closet transformer located inside a building is used to step down the voltage for the building. It is connected to a primary 4800 V AC power source. The ratio of the number of primary windings to the number of secondary windings on the transformer is 20 to 1 and 40 to 1.

a. Approximate the secondary voltage provided.

b. Approximate the current available, in amps

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(5) Compared to a PN junction with NA = ND = 1014 cm-3, which one of the following 

statements is TRUE for a PN junction with NA = ND = 1020 cm-3? ( ).

A. Reverse breakdown voltage is lower and depletion capacitance is lower 

B. Reverse breakdown voltage is higher and depletion capacitance is lower 

C. Reverse breakdown voltage is lower and depletion capacitance is higher 

D. Reverse breakdown voltage is higher and depletion capacitance is higher 

(6) Gold is often diffused into silicon PN junction devices to ( ). 

A. increase recombination rate B. reduce recombination rate 

C. make silicon a direct gap semiconductor D. make silicon semimetal

(3) Which of the following statements is (are) true about reverse bias breakdown due 

to impact ionization and Zener tunneling? ( ).

A. Tunneling breakdown generally occurs at lower voltages than impact ionization. 

B. Tunneling generally has a weaker temperature dependence that impact ionization. 

C. Significant tunneling only occurs when the junction is heavily doped. 

D. All of the above. 

(4) Consider an abrupt PN junction. Let Vbi be the built-in potential of this junction and 

VR be the applied reverse bias. If the junction capacitance (Cj) is 1 pF for Vbi + VR = 

1 V, then for Vbi + VR = 4 V, Cj will be ( ).

A. 4 pF B. 2 pF C. 0.25 pF D. 0.5 pF