Engineering Mechanics and Applied Mechanics
What this domain tests
Engineering Mechanics and Applied Mechanics tests equilibrium and motion: free-body diagrams, reactions, trusses, friction, centroids, and the dynamics topics of kinematics, energy, momentum and circular motion.
Core rules
- A body in equilibrium satisfies ΣF = 0 and ΣM = 0. Take moments about a support to eliminate one unknown reaction.
- Draw the free-body diagram before writing equations: replace supports with their reactions, include weight at the centroid, and show friction opposing impending motion.
- For a simply supported beam, reactions come from moment equilibrium; the bending moment is maximum where shear passes through zero, often under a point load.
- Trusses: method of joints suits few members; method of sections suits a cut through three members. Assume members are two-force members.
- Motion: use v = u + at, s = ut + ½at² and v² = u² + 2as for constant acceleration; use work-energy or impulse-momentum when acceleration is not constant.
- Friction: limiting friction F = μN applies at impending motion; kinetic friction is lower and acts while sliding.
Worked example
A 6 m simply supported beam carries a 12 kN point load 2 m from A. Taking moments about B: R_A × 6 = 12 × 4, so R_A = 8 kN; ΣF gives R_B = 4 kN. Maximum bending moment occurs under the load: M = 8 × 2 = 16 kN m. Check from the other side: 4 × 4 = 16 kN m.
Traps
Forgetting self-weight; using the sloping length instead of the perpendicular distance; sign errors in moment equations; mixing kN and N; treating a roller as a fixed support; applying limiting friction when the body is already sliding.