A tractor operated single acting trailing type disc harrow has 8 discs on each gang. The gang angle of both the gangs is maintained at 35°. The horizontal component of resultant soil reaction force on each disc is 600 N and it makes an angle of 30° with the gang axis. If the speed of operation is 6 km h⁻¹, the required drawbar power in kW to operate the harrow will be _______________
Official Answer Key:
15.94
Step-by-Step Solution & Explanation
Total discs (both gangs) = 2×8 = 16. Each disc's resultant soil reaction force (600 N) makes 30° with its own gang axis, and the gang axis itself is set at 35° to the direction of travel. Taking the net angle between the force vector and the direction of travel as the DIFFERENCE of these two angles (35°−30°=5°, i.e., the force is nearly aligned with the direction of travel — the physically consistent reading given the realistic power magnitude that results):
Draft (force component along travel) per disc = 600×cos(5°) = 597.7 N.
Total draft = 16×597.7 = 9563 N.
Speed = 6 km/h = 1.667 m/s.
Drawbar power = Draft×speed = 9563×1.667 = 15,939 W ≈ 15.94 kW.
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