A football coach sits on a sled while two of his players build their strength by dragging the sled across the field with ropes. The friction force on the sled is 1000 N, the players have equal pulls, and the angle between the two ropes is 20°. How hard must each player pull to drag the coach at a steady 2.0 m/s?
Ch 06: Dynamics I: Motion Along a Line
6장, 문제 1a
The three ropes in FIGURE EX6.1 are tied to a small, very light ring. Two of these ropes are anchored to walls at right angles with the tensions shown in the figure. What are the magnitude and direction of the tension T3 in the third rope?

검증된 단계별 안내1
Identify the forces acting on the ring. The ring is in equilibrium, meaning the net force in both the horizontal (x) and vertical (y) directions must be zero. The forces are T1, T2, and T3, where T1 and T2 are given, and T3 is the unknown tension we need to find.
Resolve the forces T1 and T2 into their components. Since T1 and T2 are at right angles to each other, T1 contributes only to the horizontal direction (x-axis), and T2 contributes only to the vertical direction (y-axis). Write the components as: T1x = T1, T1y = 0, T2x = 0, T2y = T2.
Express the components of T3. Let T3 make an angle θ with the horizontal. Its components are: T3x = T3 * cos(θ) and T3y = T3 * sin(θ).
Apply the equilibrium conditions. For the x-direction: T1 - T3 * cos(θ) = 0. For the y-direction: T2 - T3 * sin(θ) = 0. These two equations will allow you to solve for T3 and θ.
Solve the system of equations. From the x-direction equation, solve for T3 * cos(θ) = T1. From the y-direction equation, solve for T3 * sin(θ) = T2. Use the Pythagorean identity (cos²(θ) + sin²(θ) = 1) to find T3, and then use trigonometric ratios to find θ.

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주요 개념
질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.
Equilibrium of Forces
In physics, an object is in equilibrium when the net force acting on it is zero. This means that all the forces acting on the object balance each other out. In the context of the question, the ring is subjected to tensions from three ropes, and the equilibrium condition will help determine the unknown tension T3 by ensuring that the sum of the forces in both the horizontal and vertical directions equals zero.
추천 영상:
가이드 코스
Equilibrium
Vector Addition
Vector addition is the process of combining two or more vectors to determine a resultant vector. Each tension in the ropes can be represented as a vector with both magnitude and direction. To find the tension T3, one must consider the vectors of the known tensions and apply vector addition to solve for the unknown tension, ensuring that the resultant vector maintains the equilibrium condition.
추천 영상:
가이드 코스
Vector Addition By Components
Trigonometric Relationships
Trigonometric relationships are essential in resolving forces into their components, especially when dealing with angles. In this scenario, if the tensions are not aligned with the coordinate axes, trigonometric functions such as sine and cosine will be used to break down the tensions into their horizontal and vertical components. This breakdown is crucial for applying the equilibrium conditions effectively.
추천 영상:
가이드 코스
Trigonometry
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