Subtopic: Functional requirements, principles of working, construction and operation of manual, animal, tractor and renewable energy operated equipment for tillage, sowing, planting, fertilizer application, inter-cultivation, spraying, mowing, chaff cutting, harvesting and threshing
Question Statement:
A tractor PTO driven rotavator with a rotor radius 30 cm has 20 L-shaped blades each of width 12 cm. These blades are fixed at a radial distance of 7 cm from the center of the rotor shaft to the brackets attached to the rotor shaft. When this rotavator is operated at a forward speed of 4.5 km·h⁻¹ and at a depth of 12 cm, the resultant soil force of 150 N tangential to the rotor circumference acts at the middle of the blade width. The torsional moment acting on the blade in N·m is ______. [round off to one decimal place]
Official Answer Key:
8.90 to 9.10
Step-by-Step Solution & Explanation
The 150 N tangential soil force acts at the mid-point of the blade's WIDTH (12 cm), offset from the blade shank's central plane by half the blade width. This offset creates a twisting (torsional) moment about the blade shank's own axis: T = F × (width/2) = 150 × (0.12/2) = 150 × 0.06 = 9.0 N·m. (The rotor radius 30 cm and bracket radius 7 cm are given to compute other performance parameters such as torque about the main rotor shaft, and are not needed for the blade's own torsional moment.)
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