Explanation

Friction depends on surface roughness and nature of materials; wet surfaces reduce friction.

Rubber on wet concrete has a much lower friction coefficient compared to dry or metallic surfaces.

Wet surfaces reduce friction significantly.

Explanation

Apparent weight = Normal force; when a lift accelerates downward, the normal force decreases.

If the lift moves downward with acceleration a, apparent weight = W−ma, which is less than the real weight.

Downward acceleration reduces apparent weight.

Explanation

Impulse J=F⋅Δt represents the change in momentum of an object.

It is directly proportional to the force applied and the time duration of application.

Impulse measures the effect of force over a time interval.

Explanation

Both energy and work have SI units of joule (kg·m²/s²).

Work done is a way of transferring energy from one body to another.

Energy and work are dimensionally identical.

Explanation

A floating object arranges itself to reach stable equilibrium, minimizing potential energy.

For a table, the center of buoyancy below the center of gravity makes it float legs upwards.

Floating objects orient to achieve stable equilibrium.

Explanation

According to Archimedes’ principle, the buoyant force acts vertically upward through the center of the displaced fluid.

This point is called the center of buoyancy and determines stability of floating bodies.

Buoyant force always acts through the centroid of the displaced liquid.

Explanation

Mach number is defined as the ratio of the flow velocity to the speed of sound in the medium.

It indicates whether the flow is compressible (high Mach number) or incompressible (low Mach number).

High Mach number → compressibility effects are significant.

Explanation

Cast iron contains graphite flakes that act as lubricants, reducing tool wear during machining.

Its brittle nature allows easy cutting without much deformation.

Cast iron is the easiest to machine among common metals.

Explanation

Molten metal is poured into a reusable metallic mould using gravity, not pressure.

This method produces accurate shapes with smooth surfaces.

It is used for medium production runs.

Permanent mould casting relies on gravity to fill the mould.

Explanation

Steel is forged above its recrystallisation temperature (around 1100 °C) to improve ductility and avoid cracks.

Hot forging refines the grain structure and enhances mechanical properties.

Forging is a hot working process done above recrystallisation temperature.