Equation for uniform acceleration in Double Atwood

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Double Atwood machine.

We are able to derive an equation for the acceleration by using force analysis. If we consider a massless, inelastic string and an ideal massless pulley the only forces we can consider are the two tension forces ( ), and the weights of the three masses ( ). To find the accelerations we need to consider the accelerations and the forces affecting each individual mass.

We know that: