Subtopic: Calculation of power, torque, fuel consumption, heat load and power losses
Question Statement:
A two-wheel drive tractor is operating a mould board plough at an average speed of 4 km h⁻¹. The draft and the rear axle torque are found to be 30 kN and 25 kN m, respectively. If the rolling radius of traction wheel is 0.7 m and the wheel slip is 20%, the tractive efficiency in percent will be
Options:
(A) 67.19
(B) 46.71
(C) 72.87
(D) 84.00
Official Answer Key:
A
Step-by-Step Solution & Explanation
Actual travel speed V = 4 km/h = 4000/3600 = 1.111 m/s.
Theoretical (no-slip) angular speed relation: actual V = rω(1−slip) ⇒ ω = V/[r(1−slip)] = 1.111/[0.7×(1−0.20)] = 1.111/0.56 = 1.984 rad/s.
Input power at axle = Torque × ω = 25 × 1.984 = 49.60 kW.
Output (drawbar) power = Draft × V = 30 × 1.111 = 33.33 kW.
Tractive efficiency = Output/Input × 100 = 33.33/49.60 × 100 = 67.2%. Matches option (A) closely (rounding to 67.19).
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