Mechanical Engineering
Scope
Mechanical Engineering tests mechanics, materials, machine elements, power transmission, manufacturing, and safety. Questions often require gear-ratio calculation, torque and speed reasoning, or selection of an appropriate machine element.
Core rules
- Gear ratio = driven teeth / driver teeth. Speed changes inversely with ratio; ideal torque changes directly.
- Mechanical efficiency reduces output power or torque: output = input x efficiency.
- Stress = force / area; strain is deformation per original length.
- Bearings support rotating shafts and reduce friction; couplings connect shafts while allowing some misalignment.
- Lockout and machine guarding are required before maintenance or jam clearing.
Worked example
A 20-tooth driver gear turns at 1,200 rpm and drives a 40-tooth gear. Ratio = 40 / 20 = 2. Output speed = 1,200 / 2 = 600 rpm. If input torque is 10 Nm and efficiency is 90%, ideal output torque = 10 x 2 = 20 Nm; actual output torque = 20 x 0.90 = 18 Nm. Reasoning: the larger driven gear turns slower but with higher torque, minus losses.
Traps
Applying the gear ratio in the wrong direction reverses speed and torque. Ignoring efficiency overstates output. Mixing units such as Nm and N/mm causes calculation errors. Removing a guard to clear a jam violates safety rules.