In the figure a smooth pulley of negligible weight is...

In the figure a smooth pulley of negligible weight is suspended by a spring balance. Weights of $1 \mathrm{~kg}$ and $5 \mathrm{~kg}$ are attached to the opposite ends of a string passing over the pulley and move with acceleration because of gravity. During their motion, the spring balance reads a weight of [a) $6 \mathrm{~kg}$ (b) less than $6 \mathrm{~kg}$ (c) more than $6 \mathrm{~kg}$ (d) may be more or less than $6 \mathrm{~kg}$

In the figure a smooth pulley of negligible weight is suspended by a spring balance. Weights of $1 \mathrm{~kg}$ and $5 \mathrm{~kg}$ are attached to the opposite ends of a string passing over the pulley and move with acceleration because of gravity. During their motion, the spring balance reads a weight of
[a) $6 \mathrm{~kg}$
(b) less than $6 \mathrm{~kg}$
(c) more than $6 \mathrm{~kg}$
(d) may be more or less than $6 \mathrm{~kg}$

Key Concepts

Atwood Machine

An Atwood machine is a classic physics apparatus consisting of two masses connected by a string that passes over a pulley. Its analysis involves understanding how the difference in weights causes acceleration and how the tensions in the string behave. This concept is fundamental when examining systems in motion under gravity.

Tension in the String

Tension is the force transmitted through the string that connects two masses over a pulley. In an ideal, frictionless pulley with a massless string, the tension remains uniform on both sides even when the system is accelerating. Determining this tension is crucial for analyzing the net force transmitted to other components, such as a spring balance supporting the pulley.

Newton's Second Law

Newton's Second Law, which states that force equals mass times acceleration (F = ma), is applied to each mass in the system to determine both the acceleration of the masses and the tension in the string. This law provides the framework for analyzing the forces acting on each mass and the overall dynamics of the system.

Force on the Support

The net force acting on the pulley, which is transmitted to the spring balance, is the sum of the tensions from each side of the string. This concept involves understanding that while individual masses accelerate, the total force measured by the support (or spring balance) is determined by these tensions. This analysis is essential for predicting how a support or measuring device would register the forces in a dynamic system.

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