The slender bar AB weighs 50 lb and moves in the vertical plane. The bar was initially held at rest at 0= 30°, when a 20-lb force is suddenly applied at A. Find the forces on the rollers at points A and B. The rollers can be considered smooth and of negligible mass.

Structural Analysis
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Author:KASSIMALI, Aslam.
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Chapter2: Loads On Structures
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### Problem Statement

A slender bar \( AB \) weighs 50 lb and moves in the vertical plane. Initially, the bar is at rest with an angle \( \theta = 30^\circ \), when a 20-lb force is suddenly applied at point \( A \). Determine the forces on the rollers at points \( A \) and \( B \). The rollers are considered smooth and of negligible mass.

### Diagram Explanation

The diagram illustrates a slender bar labeled \( AB \) with point \( A \) at the top right and point \( B \) at the bottom left. A force of 20 lb is applied horizontally to the right at point \( A \). The bar is at an angle \( \theta = 30^\circ \) from the vertical axis \( y \). 

The pivot points \( A \) and \( B \) are supported by smooth rollers, implying that frictional forces are negligible. The bar’s center of mass \( G \) is depicted at the midpoint, noted by distances \( \frac{L}{2} \) along its length, with \( L \) being the total length of bar \( AB \).

The diagram includes a coordinate system with the \( x \)-axis horizontal and the \( y \)-axis vertical, intersecting through point \( B \).

### Analysis

To solve for the forces at \( A \) and \( B \), consider the following approach:

1. **Free Body Diagram**: 
   - Identify forces: weight of the bar (50 lb acting downward at \( G \)), applied force (20 lb at \( A \)), and reaction forces at \( A \) and \( B \).
   
2. **Equilibrium Equations**: 
   - Use the equations of static equilibrium (sum of forces in \( x \) and \( y \) directions, and sum of moments about a point) to find unknown forces.

3. **Moment Calculation**: 
   - Calculate moments about either \( A \) or \( B \) to simplify solving for reaction forces.

This physical interpretation and subsequent calculations will help understand the bar's response under the given force.
Transcribed Image Text:### Problem Statement A slender bar \( AB \) weighs 50 lb and moves in the vertical plane. Initially, the bar is at rest with an angle \( \theta = 30^\circ \), when a 20-lb force is suddenly applied at point \( A \). Determine the forces on the rollers at points \( A \) and \( B \). The rollers are considered smooth and of negligible mass. ### Diagram Explanation The diagram illustrates a slender bar labeled \( AB \) with point \( A \) at the top right and point \( B \) at the bottom left. A force of 20 lb is applied horizontally to the right at point \( A \). The bar is at an angle \( \theta = 30^\circ \) from the vertical axis \( y \). The pivot points \( A \) and \( B \) are supported by smooth rollers, implying that frictional forces are negligible. The bar’s center of mass \( G \) is depicted at the midpoint, noted by distances \( \frac{L}{2} \) along its length, with \( L \) being the total length of bar \( AB \). The diagram includes a coordinate system with the \( x \)-axis horizontal and the \( y \)-axis vertical, intersecting through point \( B \). ### Analysis To solve for the forces at \( A \) and \( B \), consider the following approach: 1. **Free Body Diagram**: - Identify forces: weight of the bar (50 lb acting downward at \( G \)), applied force (20 lb at \( A \)), and reaction forces at \( A \) and \( B \). 2. **Equilibrium Equations**: - Use the equations of static equilibrium (sum of forces in \( x \) and \( y \) directions, and sum of moments about a point) to find unknown forces. 3. **Moment Calculation**: - Calculate moments about either \( A \) or \( B \) to simplify solving for reaction forces. This physical interpretation and subsequent calculations will help understand the bar's response under the given force.
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