GATE 2021 AG – Question 52
A PTO rotavator has 30 cm rotor radius,20 L-blades of 12 cm width, attached at 7 cm radial distance. Forward speed 4.5 km/h, depth 12 cm. A 150 N tangential soil force acts at mid-blade width. Find blade torsional moment in N m, to one decimal.
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Correct answer: 8.90 to 9.10
Explanation
Torsion about the blade’s supporting shank acts with transverse lever arm half the12 cm blade width=.06 m. Thus $M_t=150(.06)=\mathbf{9.0}$ N m. Rotor radius would be relevant to shaft-driving torque, not the local twisting moment requested here.