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Ch 07: Newton's Third Law
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoKnight Calc 5th EditionCh 07: Newton's Third LawProblema 17b
Capitolo 7, Problema 17b

FIGURE EX7.17 shows two 1.0 kg blocks connected by a rope. A second rope hangs beneath the lower block. Both ropes have a mass of 250 g. The entire assembly is accelerated upward at 3.0 m/s2 by force F. What is the tension at the top end of rope 1?

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Step 1: Identify the forces acting on the system. The system consists of two blocks (each 1.0 kg) and two ropes (each 0.25 kg). The forces include the gravitational force acting downward on each block and rope, and the upward force F exerted to accelerate the system.
Step 2: Calculate the total mass of the system. Add the masses of the two blocks and the two ropes: \( m_{total} = m_{block1} + m_{block2} + m_{rope1} + m_{rope2} \).
Step 3: Determine the net force required to accelerate the system upward. Use Newton's second law \( F_{net} = m_{total} \cdot a \), where \( a \) is the acceleration (3.0 m/s²).
Step 4: Analyze the tension at the top end of rope 1. The tension at this point must support the weight of the lower block, the lower rope, and provide the force necessary to accelerate them upward. Use \( T_{rope1} = (m_{block2} + m_{rope2}) \cdot (g + a) \), where \( g \) is the acceleration due to gravity (9.8 m/s²).
Step 5: Substitute the values for \( m_{block2} \), \( m_{rope2} \), \( g \), and \( a \) into the equation from Step 4 to find the tension at the top end of rope 1.

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Newton's Second Law of Motion

Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This relationship is expressed by the equation F = ma, where F is the net force, m is the mass, and a is the acceleration. In this scenario, understanding how the forces acting on the blocks relate to their acceleration is crucial for calculating tension.
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Intro to Forces & Newton's Second Law

Tension in a Rope

Tension is the force transmitted through a rope or string when it is pulled tight by forces acting at either end. In a system of connected objects, the tension varies depending on the mass of the objects and the acceleration of the system. Calculating the tension at different points in the rope requires considering the weight of the blocks and the net force acting on them.
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Calculating Tension in a Pendulum with Energy Conservation

Free Body Diagram

A Free Body Diagram (FBD) is a graphical representation used to visualize the forces acting on an object. It helps in identifying all the forces, including gravitational force, tension, and any applied forces. For this problem, drawing FBDs for each block will aid in understanding how the forces interact and will facilitate the calculation of the tension in the ropes.
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Free-Body Diagrams
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