Detailed Analysis of Tyre Ballasting:

• Liquid Ballasting Standard (Option 3): In tractor operations, drive wheel traction is increased and wheel slippage is reduced by adding ballast. For liquid ballasting (water or a water + calcium chloride anti-freeze solution), the tyre tube is filled to exactly $75\%$ of its total internal volume (up to the level of the valve stem when rotated to the top).
• Air Cushion: The remaining $25\%$ volume is filled with compressed air to act as a pneumatic cushion and absorb ground shock loads. Filling more than $75\%$ results in an excessively stiff tyre with poor ride quality and risk of rim damage.

Weight transfer from the front axle to the rear drive axle of a tractor is caused by the moment created by the horizontal drawbar pull ($P$) acting at hitch height ($h$) and the drive wheel torque: $\Delta W = \frac{P \times h}{x}$. Option analysis: (A) Application of drawbar pull is the primary cause of dynamic weight transfer. (B) Tractor force is a vague non-technical term. (C) Tractor slip is a kinematic result of traction, not the cause of weight transfer. (D) Operator weight is static ballast.

In vehicle dynamics, a spatial rigid body such as a tractor chassis possesses six degrees of freedom in three-dimensional space: three translational motions (surge, sway, heave along $x, y, z$ axes) and three rotational motions (roll, pitch, yaw about $x, y, z$ axes). Option analysis: (A) Two DOF is a simplified quarter-car model. (B) Four DOF is a planar half-car (bounce and pitch) model. (C) Six degrees of freedom represents full 3D rigid body tractor dynamics. (D) Eight DOF includes sub-assemblies like cabin/seat.

According to ergonomic guidelines for agricultural hand-tool design, a power tool or manual implement supported entirely by one hand during sustained continuous operation should not exceed $2\text{ kg}$ (ideally $\lt 1.5\text{ kg}$) to avoid severe muscle fatigue, tendon strain, and musculoskeletal disorders. Option analysis: (A) $4\text{ kg}$ requires two hands or mechanical support. (B) $3\text{ kg}$ exceeds single-hand continuous support limit. (C) $2\text{ kg}$ is the standard ergonomic limit for unsupported single-hand tools. (D) $1\text{ kg}$ is ultra-light.