Mechanical Engineering Answers

A double riveted lap joint is made between 15mm thick plates. The rivet diameter and pitch are 25 mm and 75 mm, respectively. If the ultimate stresses are 400 MPa in tension, 320 MPa in shear and 640 MPa in crushing, find the minimum force per pitch which will rupture the joint. If the above joint is subjected to a load such that the factor of safety is 4, find out the actual stresses developed in the plates and rivets.

10.Determine the maximum mean diameter of a taper in for use to fix a lever to a

shaft. If it transmit a maximum torque of 750 in-lb. The shaft diameter is 3in.

3. A 4.3in diameter by 3in long journal bearing is to carry a 6600lb load at 4600

r[, isomg SAE 40 lube oil at 200 through a single hole at 25 psi. Compute

the bearing pressure. Bearing pressure is the same as bearing stress.

( Ans Sb=511.63psi )

1. A steel tie rod on bridge be made withstand a pull of 3500lbs. find the

diameter of the rod assuming a factor of safety of 2.5 and ultimate stress of

5700psi.

( Ans d=1.398 in. )

A steady stream of air enters a horizontal compressor at the rate of 0.02 kg/s. The air temperature is 10o C at entry and 300o C at exit. The velocity of the air is 30 m/s at entry and 6 m/s at exit. During its passage through the compressor, the air experiences a heat loss of 105 kJ/kg of air. Calculate:

(a) The change in kinetic energy per kg of air

(b) The change in enthalpy per kg of air

(c) The work done per kg of air

(d) The power required to drive the compressor

(e) The volume of air entering the compressor per second

(f) The flow area of the entry pipe if the entry pressure is 1 bar Take R = 0.287 kJ/kgK and cp = 1.005 kJ/kgK

Question 1

A horizontal "hot air blower" consists of a fan, an electrical heating element and a nozzle

The power input to the fan is 50 J/s and the power input to the heating element is 1.44 kJ/s. The air enters the fan with negligible velocity at a pressure of 1 bar and a temperature of 20 C, the volumetric flow rate being 0.5 m3 /min. After passing over the heating element, the air leaves the nozzle with a velocity of 25 m/s and a pressure of 1.1 bar. Treating the complete arrangement as a steady flow system and ignoring any heat loss from the system, determine:

(a) The mass flow rate of air entering the fan in kg per second (b) The kinetic energy of the air leaving the nozzle per second

(c) The change in enthalpy of the air occurring per second between entering the fan and leaving the nozzle

(d) The temperature of the air as it leaves the nozzle. (e) The density of the air as it leaves the nozzle

(f) The flow area at the nozzle exit.

Take R = 0.287 kJ/kgK and cp = 1.005 kJ/kgK

5.) A student will receive P3,000 at the beginning of each 3 months for 4 years. What is the sum of

this annuity at the end of the 4th year if the interest rate is 6% compounded quarterly?

Ans. 54,604.07

5.) A student will receive P3,000 at the beginning of each 3 months for 4 years. What is the sum of

this annuity at the end of the 4th year if the interest rate is 6% compounded quarterly?

Ans. 54,604.07

4.) An engineer is entitled to receive P25,000 at the beginning of each year for 18 years. If the rate of

interest is 4% compounded annually.

1. What is the present value of this annuity at the time he is supposed to receive the first

payment?

2. What is the sum of this annuity at the end of the 18th year?

3. Find the difference between the sum of this annuity which is paid at the beginning of

each year and an annuity paid at the end of each year.

Ans. 1. P329,141.72 2. P666,780.73 3. P25,645.41

2.) A businessman is faced with the prospect of fluctuating future budget for the maintenance of the

generator. During the first 5 years, P1,000 per year will be budgeted. During the second five

years, the annual budget will be P1,500 per year. In addition, P3,500 will be budgeted for an

overhaul of the machine at the end of the fourth year and another P3,500 for an overhaul at the

end of 8th year. Assuming compound interest at 6% per annum, what is the equivalent annual cost

of maintenance?

Ans. P1,888.87