Two identical bodies of mass \(m\) are connected by a spring of stiffiness \(k\) and constrained to move in rectilinear motion as shown. Derive the equations of motion for the system.

Short Answer

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Question: Derive the equations of motion for a system consisting of two identical bodies of mass \(m\) connected to a spring of stiffness \(k\). Answer: The equations of motion for the given system are: \(m x_1'' + k(x_1 - x_2) = 0\) \(m x_2'' + k(x_2 - x_1) = 0\)

Step by step solution

01

Write down the general equations

Newton's second law of motion states that the force acting on an object is equal to its mass times its acceleration: \(F = ma\). Hooke's law states that the force exerted by a spring is proportional to its displacement from the equilibrium position: \(F = -kx\). In this problem, we need to find the equations of motion for the two bodies. Let \(x_1\) and \(x_2\) denote the displacements of mass 1 and mass 2 from their respective equilibrium positions, such that the positive direction is to the right.
02

Identify the forces acting on each mass

For mass 1, there are two forces acting on it: the force due to the spring connecting it to mass 2, and the force due to its own inertia. According to Hooke's law, the force exerted by the spring is \(-k(x_1 - x_2)\), where the negative sign indicates that the force is always directed toward the equilibrium position. The force due to its own inertia is simply \(-mx_1''\). For mass 2, there are two forces acting on it: the force due to the spring connecting it to mass 1, and the force due to its own inertia. According to Hooke's law, the force exerted by the spring is \(-k(x_2 - x_1)\), where the negative sign indicates that the force is always directed toward the equilibrium position. The force due to its own inertia is simply \(-mx_2''\).
03

Apply Newton's second law

Now, we will apply Newton's second law for each mass: For mass 1: \(-k(x_1 - x_2) = m x_1''\) For mass 2: \(-k(x_2 - x_1) = m x_2''\)
04

Rewrite the equations in a standard form

We can rewrite the equations from Step 3 as follows: Mass 1: \(m x_1'' + k(x_1 - x_2) = 0\) Mass 2: \(m x_2'' + k(x_2 - x_1) = 0\)
05

Combine the equations to obtain the final result

These two equations represent the equations of motion for the system of two identical masses connected by a spring: \(m x_1'' + k(x_1 - x_2) = 0\) \(m x_2'' + k(x_2 - x_1) = 0\) These are the differential equations that describe the motion of the two masses in the given system.

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