Introduction to Mechanics Examples

Ten progressively more demanding applications of the modeling and vector concepts introduced in the theory lesson.

Classifying Scalars and Vectors

A floor slab has an area of 180 m2180\ \text{m}^2, while a façade tie carries a 24.0 kN24.0\ \text{kN} force directed 20∘20^\circ above the horizontal. Classify the quantities.

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Weight of a Precast Panel

A precast panel has mass m=2500 kgm=2500\ \text{kg}. Determine its weight using g=9.81 m/s2g=9.81\ \text{m/s}^2.

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Resolve a Diagonal Brace Force

A brace exerts F=100 kNF=100\ \text{kN} at 30∘30^\circ above the positive horizontal axis. Determine FxF_x and FyF_y.

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Resultant of Perpendicular Cable Forces

Two cables pull a ring with 40.0 kN40.0\ \text{kN} to the right and 30.0 kN30.0\ \text{kN} upward. Determine the resultant magnitude and direction.

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Choose a Particle Idealization

Several cables meet at a compact roof-ring connection. The goal is only to determine the cable tensions from concurrent forces. Select the appropriate idealization.

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Choose a Rigid-Body Idealization

Wind acts on a canopy and the design question is whether the canopy tends to rotate about its supports. Should the canopy be modeled as a particle or rigid body?

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Identify a Newton Third-Law Pair

A chandelier pulls downward on its suspension cable with 8.00 kN8.00\ \text{kN}. State the third-law partner force.

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Check Dimensional Consistency

A draft calculation proposes F=ma+vF=ma+v, where mm is mass, aa is acceleration, and vv is velocity. Determine whether the equation can be physically valid.

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Apply the Principle of Transmissibility

A rigid frame is pulled by an 18.0 kN18.0\ \text{kN} force. First, the force is moved to another point on the same line of action. Then consider moving it to a parallel line 0.750 m0.750\ \text{m} away. Determine when the two representations are statically equivalent.

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Decide Whether a Static Model Is Appropriate

An elevator car is accelerating upward at 1.20 m/s21.20\ \text{m/s}^2. A preliminary calculation proposes treating the resultant force as zero to determine the cable force. Is that static idealization valid?

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Sign Convention Reminder

Before resolving any force, define the positive coordinate directions. A negative component means the actual component acts opposite the assumed positive axis; it does not mean the force magnitude is physically negative.