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Ch 05: Applying Newton's Laws
Chapter 5, Problem 5

A large wrecking ball is held in place by two light steel cables (Fig. E5.6). If the mass m of the wrecking ball is 3620 kg, what are (a) the tension TB in the cable that makes an angle of 40° with the vertical and (b) the tension TA in the horizontal cable?Diagram showing a wrecking ball held by two cables, with angles and tensions labeled.

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1
Identify the forces acting on the wrecking ball: the gravitational force (mg), the tension in the horizontal cable (T_A), and the tension in the inclined cable (T_B).
Resolve the tension T_B into its vertical and horizontal components. The vertical component is T_B * cos(40°) and the horizontal component is T_B * sin(40°).
Set up the equilibrium equations for the vertical and horizontal directions. For vertical equilibrium: T_B * cos(40°) = mg. For horizontal equilibrium: T_A = T_B * sin(40°).
Solve the vertical equilibrium equation for T_B: T_B = mg / cos(40°).
Substitute the value of T_B into the horizontal equilibrium equation to find T_A: T_A = (mg / cos(40°)) * sin(40°).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Tension in Cables

Tension is the force exerted along a cable or rope when it is pulled tight by forces acting from opposite ends. In this scenario, the tension in the cables must balance the weight of the wrecking ball, which is determined by its mass and the acceleration due to gravity. Understanding how tension distributes in multiple cables is crucial for solving the problem.
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Equilibrium of Forces

An object is in equilibrium when the sum of all forces acting on it is zero. For the wrecking ball, this means that the vertical components of the tensions in the cables must equal the weight of the ball, while the horizontal components must cancel each other out. This principle allows us to set up equations to solve for the unknown tensions.
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Trigonometric Functions

Trigonometric functions, such as sine and cosine, relate the angles of a triangle to the ratios of its sides. In this problem, these functions are used to resolve the tension forces into their vertical and horizontal components based on the angles given. This is essential for applying the equilibrium conditions to find the tensions in the cables.
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Related Practice
Textbook Question
A 45.0-kg crate of tools rests on a horizontal floor. You exert a gradually increasing horizontal push on it, and the crate just begins to move when your force exceeds 313 N. Then you must reduce your push to 208 N to keep it moving at a steady 25.0 cm/s. (a) What are the coefficients of static and kinetic friction between the crate and the floor?
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Textbook Question
A 45.0-kg crate of tools rests on a horizontal floor. You exert a gradually increasing horizontal push on it, and the crate just begins to move when your force exceeds 313 N. Then you must reduce your push to 208 N to keep it moving at a steady 25.0 cm/s. (b) What push must you exert to give it an acceleration of 1.10 m/s2?
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Textbook Question
A 1130-kg car is held in place by a light cable on a very smooth (frictionless) ramp (Fig. E5.8). The cable makes an angle of 31.0° above the surface of the ramp, and the ramp itself rises at 25.0° above the horizontal. (b) Find the tension in the cable.

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Textbook Question
A box of bananas weighing 40.0 N rests on a horizontal surface. The coefficient of static friction between the box and the surface is 0.40, and the coefficient of kinetic friction is 0.20. (a) If no horizontal force is applied to the box and the box is at rest, how large is the friction force exerted on it?
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Textbook Question
A box of bananas weighing 40.0 N rests on a horizontal surface. The coefficient of static friction between the box and the surface is 0.40, and the coefficient of kinetic friction is 0.20. (b) What is the magnitude of the friction force if a monkey applies a horizontal force of 6.0 N to the box and the box is initially at rest?
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Textbook Question
A box of bananas weighing 40.0 N rests on a horizontal surface. The coefficient of static friction between the box and the surface is 0.40, and the coefficient of kinetic friction is 0.20. (c) What minimum horizontal force must the monkey apply to start the box in motion?
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