Farm Machinery, Irrigation & Post-Harvest

Classification of farm operations by power source mobility:

• Stationary operations: Irrigation water lifting (pumpsets), winnowing (winnowing fans), and threshing (stationary power threshers) are carried out at a fixed location using stationary engines or electric motors.
• Tractive/Mobile operations: Harvesting (combines/reapers), cultivation (ploughing, harrowing), and transportation require mobile, tractive power units (tractors or draught animals).

A combine harvester is a massive, multi-functional agricultural machine that integrates reaping, threshing, separating, and winnowing in a single continuous field operation. It demands high mechanical energy (typically $60\text{ to }\gt 150\text{ hp}$) and engine systems that far exceed the draft power capability of draft animals (a pair of bullocks typically produces only about $0.75\text{ to }1.0\text{ hp}$ of sustained power).

Option analysis:

• Disk Harrow: Light bullock-drawn disk harrows are widely used in smallholder agriculture.
• Weeder: Animal-drawn interculture weeders and sweeps are routinely operated.
• Cultivator: Animal-drawn spring or rigid-tine cultivators are standard farm implements.
• Combine Harvester: Correct, requires high mechanical/diesel engine power and cannot be animal-drawn.

Power transmitted by a belt drive:

• Given data:
  Pulley diameter $D = 1\text{ m}$
  Rotational speed $N = 500\text{ rpm}$
  Tight side tension $T_1 = 50\text{ kgf}$
  Slack side tension $T_2 = 20\text{ kgf}$
  Effective tension $(T_1 - T_2) = 50 - 20 = 30\text{ kgf}$
• Belt velocity ($v$):
  $v = \frac{\pi D N}{60} = \frac{\pi \times 1 \times 500}{60} = \frac{500\pi}{60} = 26.1799\text{ m/s}$
• Power in metric horsepower ($1\text{ hp} = 75\text{ kgf}\cdot\text{m/s}$):
  $\text{Power} = \frac{(T_1 - T_2) \times v}{75} = \frac{30 \times 26.1799}{75} = \frac{785.397}{75} = 10.472\text{ hp} \approx 10.47\text{ hp}$.
  
  Option analysis:
• 17.44 hp: Result if tension difference is taken as $50\text{ kgf}$.
• 6.98 hp: Result if tension difference is taken as $20\text{ kgf}$.
• 10.47 hp: Correct calculated power transmission.
• 628 hp: Numerical error omitting conversion factors.