Agricultural and Biosystems Engineers Licensure Examination (ABELE) · Philippines · Professional Regulatory Board of Agricultural and Biosystems Engineering, PRC
Original practice questions written to the published syllabus · not past papersHow mechanisms move and transmit power: linkages, cams, gears, belts, flywheels, governors, balancing and vibration.
In the exams: GATE AG Sections 2 and 3 (power transmission, belts and gears recur); ICAR AIEEA-PG Unit III
Agricultural and Biosystems Engineers Licensure Examination (ABELE)
Power and machinery allied subjects: pulley and belt sizing, gear and sprocket ratios for farm machinery drives, power transmission and prime-mover matching.
How our questions for Agricultural and Biosystems Engineers Licensure Examination spread across the units of Theory of Machines. Difficulty: 9 easy, 13 medium, 3 hard.
| Belt, rope and chain drives: tension ratio and power | 7 | |
| Brakes and dynamometers | 4 | |
| Differential gear | 3 | |
| Clutches | 3 | |
| Gears and gear trains: simple, compound and epicyclic | 2 | |
| Governors | 2 | |
| Cams and followers | 1 | |
| Flywheels and turning-moment diagrams | 1 | |
| Balancing of rotating and reciprocating masses | 1 | |
| Free and forced vibrations and critical speed | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
When should a tractor operator disengage the differential lock?
A. Before turning, because a locked axle resists turning and can cause loss of steering control
The lock makes both rear wheels turn at the same speed, which is useful for traction in straight-line work on slippery ground but fights the different wheel paths on a turn. Operators' manuals therefore require it to be released before turning and when travelling at speed.
Further reading: Liljedahl et al., Tractors and Their Power Units
A belt running at 15 m/s has a tight-side tension of 1200 N and a slack-side tension of 450 N. What power does it transmit?
C. 11.25 kW
P = (T1 - T2)v = (1200 - 450) x 15 = 11 250 W = 11.25 kW. Adding the tensions gives 24.75 kW; T1 x v gives 18 kW; T2 x v gives 6.75 kW.
Further reading: Rattan, Theory of Machines
A 17-tooth sprocket on a roller chain of 15.875 mm pitch turns at 400 rpm. What is the average chain speed?
C. 1.80 m/s
Average chain speed v = pTN/60 = 0.015875 x 17 x 400/60 = 1.80 m/s: in one revolution T pitches of chain pass the sprocket. Forgetting to divide by 60 gives a per-minute figure; forgetting the tooth number gives one pitch per revolution; multiplying by 2π wrongly converts an already linear quantity.
Further reading: Rattan, Theory of Machines
Why is a variable-speed (all-speed) governor usual on farm tractors, whereas many road vehicles use a minimum-maximum governor?
B. A tractor must hold a set engine and PTO speed as field load varies; a road driver sets speed directly with the pedal
With an all-speed governor the hand throttle sets a speed and the governor adjusts fuel to hold it at any load, which keeps PTO-driven machines at their rated speed. A min-max governor controls only idle and maximum speed; in between the driver sets fuel directly. Cost and engine speed are not the reason; min-max governors are common on diesel road vehicles.
Further reading: Liljedahl et al., Tractors and Their Power Units
A thresher drum has a residual unbalance equivalent to a 50 g mass at 250 mm radius. What rotating force does this unbalance exert on the bearings at 900 rpm?
C. 111 N
F = mω²r = 0.05 x 94.25² x 0.25 = 111 N. Using rpm for ω gives 10125 N; using rev/s gives 2.81 N. The force rises with the square of speed, which is why a drum that is acceptable at low speed shakes badly at working speed. 11.3 N divides the correct force by g.
Further reading: Rattan, Theory of Machines
A grain cleaner running at 1500 rpm is to be mounted on undamped springs so that only 10% of its unbalanced force reaches the floor. What static deflection of the springs is needed?
B. 4.37 mm
Undamped TR = 1/(r² - 1) = 0.1 gives r² = 11, r = 3.317. Running frequency = 25 Hz, so fn = 25/3.317 = 7.54 Hz. δ = g/(2πfn)² = 9.81/(47.36)² = 4.37 mm. Using r² = 10 (forgetting the minus one) gives 3.98 mm; setting the natural frequency equal to the running frequency gives 0.40 mm, which would put the machine at resonance; forgetting 2π gives a deflection far too large.
Further reading: Rao, Mechanical Vibrations
A clutch transmits 300 N m at 2000 rpm without slipping. What power does it transmit?
A. 62.8 kW
P = Tω = 300 x 2π x 2000/60 = 62832 W = 62.8 kW. Multiplying torque by rpm gives 600 kW; dividing the correct answer by 2 has no basis. 31.4 kW is half the correct value; 0.6 kW multiplies torque by rpm and divides by 10⁶.
Further reading: Rattan, Theory of Machines
A tractor's single-plate dry clutch (both sides effective) must transmit 400 N m. The linings have outer and inner radii of 160 mm and 100 mm, and μ = 0.35. Assuming uniform wear, what axial spring force is needed?
D. 4396 N
T = nμW(R1 + R2)/2 gives W = T/(nμ R_mean) = 400/(2 x 0.35 x 0.13) = 4396 N. Using one surface doubles it; using the outer radius instead of the mean gives 3571 N; using R1 + R2 as the radius without halving gives 2198 N.
Further reading: Rattan, Theory of Machines
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