The two balls a and B have the same mass m and are suspended at o point by two equal length thin wires. Between the two balls is a light spring with stiffness coefficient K When the spring is in the horizontal direction and the angle between the two thin wires is θ, the length of the spring is compressed mgtan (θ / 2) / K, why not 2mgtan (θ / 2) / k

This problem can be obtained by analyzing the force on a single ball: the force on a ball is gravity, the tension of the rope and the elastic force of the spring. LZ knows that the elastic force is mgtan (θ / 2) / K, which does not explain. If only a few forces balance the force on the ball, it means that the force on the spring is mgtan (θ / 2), and the force on both ends of the spring should be the same

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