Heat & Mass Transfer

• Forces on Gang of Disc Harrows:
• Assertion (A): Concave end of the disc harrow gang tends to penetrate more deeply than the convex end. $\implies$ True.
• The soil side forces acting on disc faces create a couple that tilts the gang, causing the outer concave end to dig in deeper while the convex end tends to ride out of the soil.
• Reason (R): The radial force, which includes the vertical support force on the disc blade, must pass slightly to the rear of the disc centerline. $\implies$ True.
• Due to soil resistance and forward travel velocity, the resultant radial reaction shifts slightly rearward of the vertical center axis.
• Relationship: Reason (R) describes longitudinal force line of action on an individual blade, but does not provide the causal explanation for gang-level moments across the width.
• Conclusion: Both (A) and (R) are true but (R) is NOT the correct explanation of (A) (Option 2).

Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).

• Primary Failure Modes of Machine Gears:
• In mechanical power transmission, the predominant modes of gear tooth failure are:
• Bending fatigue: Repeated cyclic cantilever loading causing fatigue cracks to initiate at the root fillet and propagate across the tooth base.
• Surface wear: Abrasive, adhesive, or corrosive material removal across sliding tooth flanks.
• Pitting (Surface fatigue): Cyclic subsurface contact shear stresses exceeding fatigue endurance limit, causing small metal flakes to dislodge from pitch-line surfaces.
• (C) Stiff housing and (E) curved surfaces are design features, not failure mechanisms.
• Conclusion: Most gears fail from (A), (B) and (D) only (Option 2).

Correct option: (2) (A), (B) and (D) only,

• Tractor Operator Seat Ergonomics and Ride Vibration:
• Ride vibration in agricultural tractors consists of pitch, roll, and vertical bounce vibrations induced by terrain roughness.
• The Centre of Gravity (CG) of the tractor experiences the minimum angular rotational acceleration and pitch motions.
• Positioning the operator's seat as near to the centre of gravity as practical isolates the driver from severe pitching and rolling whiplash amplitudes.
• Conclusion: Near to the centre of gravity (Option 2).

Correct option: (2) Near to the centre of gravity

• AutoCAD JOIN Command:
• Function: In Computer-Aided Design (AutoCAD), the JOIN command (J) connects collinear lines, open arcs, elliptical arcs, and splines that share common endpoints into a single continuous polyline object.
• Other Commands:
• Merge: Used in layers or data sets.
• Add: Mathematical insertion.
• Combine: Boolean 3D solid modeling command.
• Conclusion: Join (Option 4).

Correct option: (4) Join