Mechanical Engineering Review Online

1. A machine is to punch 28 mm diameter hole from a 20 mm thick plate having an ultimate shearing strength 420 MPa. A flywheel is to be designed with a mean diameter of 1.2 meter, a maximum operating speed of 220 rpm, and coefficient of fluctuation of 0.12. The flywheel's hub and arm weighing may be taken to be four times its thickness. Find the flywheel weight required, in kg.

a. 532.1

b. 441.8

c. 249.2

d. 362.1

2. A flywheel releases 260 kJ of energy during operation. It has a mean diameter of 1 m and the speed changes from 280 rpm to 220 rpm during punching. The weight of the arm and hub is 12% of the rim weight with flywheel material of 0.020 kg/cm3. Calculate the width of the rim, if the thickness is 10 cm.

a. 65.32 cm

b. 76.42 cm

c. 89.84 cm

d. 55.34 cm

3. A flywheel is designed to punch 18 holes per minute. It is used to punch 2.5-in diameter hole from steel plate 1/2-in thick. If the ultimate shearing stress of the plate is 260 MPa, find the power needed to punch the hole.

a. 2.34 kW

b. 1.26 kW

c. 3.33 kW

d. 4.25 kW

4. An 800 kg flywheel changes its speed from 200 rpm to 170 rpm during punching. If the mean diameter of the flywheel is 650 mm, find the energy released by the flywheel.

a. 5.14 kJ

b. 4.25 kJ

c. 3.27 kJ

d. 2.21 kJ

5. Find the pressure needed to punch a 3.5-in diameter hole from a 1.5-in thick steel plate.

a. 420 tons

b. 332 tons

c. 562 tons

d. 275 tons

6. A 5.50 ft mean diameter flywheel has to absorb 3800 ft-lb of energy and maintain a coefficient of fluctuation of 0.10. If the mean speed is 90 ft/sec, find the weight of the flywheel.

a. 151.06 lbs

b. 231.21 lbs

c. 123.11 lbs

d. 282.09 lbs

7. A flywheel weighing 1200 kg has a radius of gyration of 1.80 m. The normal operation speed is 180 rpm and coefficient of fluctuation of 0.08. Find the kinetic energy released by the flywheel.

a. 110.52 kJ

b. 132.33 kJ

c. 162.11 kJ

d. 181.91 kJ

8. A 50-in diameter flywheel has a weight of 830 lbs. During operation, the speed is 190 rpm. If the coefficient of fluctuation is 0.88, calculate the energy released by the flywheel.

a. 3986.05 ft-lb

b. 4321.09 ft-lb

c. 3091.85 ft-lb

d. 4551.89 ft-lb

9. A 920 mm mean diameter flywheel has a width of 380 mm, 80 mm thickness and 7200 kg/m³ density. Neglecting the weight of the arm and the hub, compute for the energy released if the speed changes from 290 rpm to 240 rpm.

a. 19.45 kJ

b. 22.31 kJ

c. 16.72 kJ

d. 25.44 kJ

10. The power required to shear a plate of 60 mm thickness for 12 sec is 8 kW. If the ultimate strength of the plate material is 450 MPa, how wide should the plate be?

a. 100.1 mm

b. 192.7 mm

c. 165.3 mm

d. 118.50 mm

11. A flywheel has a rim weight of 480 kg and mean radius of 480 mm. If the rim width is 6 times the rim thickness and material density is 7300 kg/m³, calculate for the width of the flywheel.

a. 253.12 mm

b. 362.12 mm

c. 300.14 mm

d. 361.68 mm

12. A flywheel has a total weight of 600 kg and the weight of the arm and the hub is 10% of the total weight. If it has a mean diameter of 1.2 m and width of 310 mm. Determine the thickness of the flywheel if the density of the material is 7100 kg/m³.

a. 60.34 mm

b. 68.31 mm

c. 65.08 mm

d. 57.32 mm

13. The energy required to punch a hole is 3.20 kJ from a flywheel mean diameter of 850 mm that slows down to 2.8 rps to 3.5 rps during punching. If the weight of arm and hub account to 9% of the rim weight, determine the rim weight.

a. 170.25 kg

b. 186.71 kg

c. 195.55 kg

d. 220.11 kg

14. A 1.30 m mean diameter of flywheel, 480 kg weight changes its speed from 210 rpm to 230 rpm during shearing process. Calculate the force needed to shear a 28 mm thick plate.

a. 562.31 kN

b. 698.98 kN

c. 765.82 kN

d. 431.11 kN

15. A plate 180 mm wide and 25 mm thick with strength of 420 MPa is to be sheared. During the shearing process, a 900 mm mean diameter flywheel changes speed from 220 rpm to 190 rpm. Determine the weight of the flywheel to be used.

a. 1831.6 kg

b. 1973.6 kg

c. 1729.8 kg

d. 1655.2 kg

16. During a punching process of 400 kg flywheel with 1.20 m mean diameter, the speed varies from 200 rpm to 170 rpm. Find the kinetic energy required.

a. 8.76 kJ

b. 9.32 kJ

c. 7.33 kJ

d. 5.32 kJ

17. The kinetic energy needed to punch a hole is 8 kJ. What is the maximum thickness of plate that can be punched if the hole diameter is 30 mm and the ultimate stress of the plate is 450 MPa.

a. 16.25 mm

b. 17.31 mm

c. 15.77 mm

d. 19.42 mm

18. A press is used to punch 10 holes per minute of 28 mm diameter holes from a 25 mm thick plate. Find the power required to punch a hole, if the ultimate shear stress is 420 MPa.

a. 2.32 kW

b. 3.33 kW

c. 1.92 kW

d. 4.00 kW

A bearing 2.0 inches in diameter and 1.8 inches long supports a journal running at 1500 rpm. It operates satisfactorily with a diametral clearance of 0.0028 inch and a total radial load of 1420 lbs. At 150 deg F operating temperature of the oil film, the bearing modulus ZN/P was found to be 16.50.

19. Determine the bearing stress

a. 354.1 psi

b. 364.2 psi

c. 387.3 psi

d. 394.4 psi

20. Determine the viscosity.

a. 4.3

b. 3.3

c. 5.7

d. 2.2

21. A journal bearing 55 mm in diameter and 25 mm long supports a radial load of 1400 kg. If the coefficient of bearing friction is 0.012 and the journal rotates at 1000 rpm, find the horsepower loss in the bearing.

a. 0.636 hp

b. 0.778 hp

c. 0.879 hp

d. 0.572 hp

22. A 78 mm bearing using oil with an absolute viscosity of 0.70 poise running at 520 rpm gives satisfactory operation with a bearing pressure of 12 kg/cm². The bearing clearance is 0.130 mm. Find the unit pressure at which the bearing should operate if the speed is changed to 600 rpm, in kg/cm².

a. 13.85

b. 14.55

c. 12.87

d. 16.25

23. A shaft is supported by 3.5-in diameter and 4.5-in long bearing that uses oil with a viscosity of 2.8 x 10^-6 reyns. The bearing has a diametral clearance of 0.009-in. At what speed should the shaft rotate so that the friction power is limited only to 0.95 HP.

a. 3482.6 rpm

b. 4438.2 rpm

c. 2118.8 rpm

d. 5542.8 rpm

24. A shaft rotating at 1750 rpm is supported by bearing with a length of 100 mm and diameter of 65 mm. If the load is light and SAE OIL No. 20 (u=2.5 x 10^-6 reyns) is used and diametral clearance is 0.135 mm, compute the power loss due to friction.

a. 168.2 W

b. 177.8 W

c. 198.8 W

d. 185.1 W

25. A bearing, whose shaft rotates at 550 rpm, has a friction loss of 20 kW. The bearing load is 35 kN and friction of 0.15. Find the bearing diameter.

a. 100.0 mm

b. 165.8 mm

c. 132.3 mm

d. 145.8 mm

26. A bearing has a per unit load of 600 kPa. The load on the bearing is 25 kN and it has a diametral ratio of 0.0015. If the diametral clearance is 0.120 mm, find the length of the journal.

a. 535.25 mm

b. 520.81 mm

c. 547.27 mm

d. 580.96 mm

27. A bearing journal rotates at 480 rpm is used to support a load of 60 kN. It has a diameter of 25 cm and length of 45 cm. Find the friction loss in kW per bearing. Use f=0.13.

a. 24.50 kW

b. 29.22 kW

c. 35.80 kW

d. 20.11 kW

28. A bearing 160 mm diameter and 320 mm long supports a load of 6000 kg. If the coefficient of friction is 0.19, find the torque required to rotate the shaft.

a. 984.3 J

b. 894.6 J

c. 755.8 J

d. 672.8 J

29. The main bearing of one cylinder steam are 150 mm diameter by 290 mm long and support a load of 4500 kg. Find the bearing stress.

a. 403.8 kPa

b. 451.2 kPa

c. 507.4 kPa

d. 522.1 kPa

30. The main bearing of one cylinder steam are 150 mm diameter by 290 mm long and supports a load of 4200 kg. Find the bearing stress.

a. 845.2 kPa

b. 751.25 kPa

c. 988.10 kPa

d. 947.12 kPa

31. The weight of each wheel of a motor-driven travelling crane moving at 600 fpm is 5800 lbs. If the coefficient of rolling friction is 0.05, find the horsepower required to overcome rolling friction.

a. 28.91

b. 38.17

c. 24.33

d. 21.09

32. Find the desired life of a ball bearing to support a radial load of 4500 if with moderate shock and a thrust load of 2000 lb for 20 hrs per day for 10 years.

a. 62000 hrs

b. 65000 hrs

c. 78000 hrs

d. 73000 hrs

33. Compute the force necessary to move a weight of 6000 lbs supported on four steel wheels of 2.5 ft diameter, assuming the coefficient of rolling friction to be 0.007.

a. 55 lbs

b. 68 lbs

c. 77 lbs

d. 42 lbs

Answer Key (Handwritten)