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A uniform wire frame \(\mathrm{ABC}\) is in the shape of an equilateral triangle in \(x y\)-plane with centroid at the origin. (1) If \(A B\) is removed, the centre of mass of the remaining figure is in fourth quadrant. (2) If \(A C\) is removed, the centre of mass of the remaining figure is in first quadrant. (3) If \(B C\) is removed, the centre of mass of the remaining figure is on the positive \(Y\)-axis. (4) If \(A C\) is removed, the centre of mass of the remaining figure is in third quadrant.

Short Answer

Expert verified
Condition (3): Removing BC leads to the center on the positive Y-axis.

Step by step solution

01

Understand the Problem Context

An equilateral triangle in the xy-plane has its centroid at the origin (0,0). The centroid divides the medians in a 2:1 ratio. Depending on which side is removed, the center of mass will shift towards the remaining two sides.
02

Analyze Condition 1

If side AB is removed, the center of mass moves towards the other sides AC and BC. The problem states it moves to the fourth quadrant, which indicates the center of mass will have a positive x-coordinate and a negative y-coordinate.
03

Analyze Condition 2

If side AC is removed, the center of mass should move to the remaining sides AB and BC, placing the center of mass in the first quadrant. This condition requires a positive x-coordinate and a positive y-coordinate.
04

Analyze Condition 3

If side BC is removed, the center of mass moves towards AC and AB. The statement indicates the center of mass remains on the positive Y-axis, meaning the x-coordinate must be zero and the y-coordinate must be positive.
05

Analyze Correct Conditions

Evaluate and determine which conditions satisfy the given descriptions. Re-evaluate each option with the information from geometry and center of mass rules and determine the correct condition matches, if any.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Equilateral Triangle
An equilateral triangle is a special type of triangle where all three sides have the same length. This equality makes each interior angle measure exactly 60 degrees. Since it is such a symmetrical shape, it has several unique properties.
For example, if you draw a median from each vertex (a line from a corner to the midpoint of the opposite side), all three medians will intersect at a single point. This point is known as the centroid.
The side lengths, along with the equal angles, make the equilateral triangle perfect for exercises in understanding balance and symmetry, both essential in grasping the concept of the center of mass.
Centroid
In geometry, the centroid of a shape is the point where all medians intersect. In an equilateral triangle, it divides each median in a 2:1 ratio, with the longer segment lying between the vertex and the centroid.
The centroid essentially acts as a balancing point or center of mass of the shape. For the equilateral triangle lying in the xy-plane, the centroid at the origin (0,0) is key to understanding why removing one side of the triangle shifts the center of mass to particular quadrants. The symmetry of the equilateral triangle ensures that the centroid is equidistant from all sides in its complete form.
Coordinate Quadrants
In the Cartesian coordinate plane, the quadrants are split into four sections - first, second, third, and fourth. These quadrants help in determining the direction or placement of a point based on its coordinates:
  • The **first quadrant** accommodates points where both x and y coordinates are positive.
  • The **second quadrant** includes points with a negative x and a positive y value.
  • The **third quadrant** consists of points where both x and y are negative.
  • The **fourth quadrant** houses points with a positive x coordinate and a negative y coordinate.
When a side is removed from the triangle, the distribution of mass changes, shifting the center of mass towards the remaining sides. This shift can be then categorized into these quadrants based on the coordinates.
Geometry
Geometry involves the study of shapes, their sizes, and the properties and relationships of space. It includes understanding figures like triangles, circles, and polygons.
Understanding geometry is crucial in solving problems related to position and movement in space, like when examining the center of mass of a figure. It provides tools to apply logical constructs, such as medians and centroids, to understand the properties of shapes.
In this exercise, geometry helps us comprehend how removing a side of the triangular wire frame alters the gravitational pull, shifting the center of mass. Therefore, geometry isn't just about drawing shapes; it's about understanding the spatial relationships and forces at play.

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