1.

A weight of mass m hangs on a thread. The thread is deflected by an angle alpha_0and let go. Find the tension of the thread as a function of the angle alpha .

Answer»


Solution :In the DIRECTION normal to the velocity the forces acting on the weight are the tension of the thread T and the component of the force of gravity, `F_2= mg cos ALPHA`(Fig. ). ACCORDING to Newton.s second law
`T-F_(2) = mv^(2)//L`
To find the velocity apply the law of conservation of energy
`mgh_(0) = mgh +mv^2//2`
Hence
`T = mg cos alpha +(2mg)/l (h_0 -h)`
However , `h_(0) = 1 (1- cosalpha_(0)), h = l ( 1 - cos alpha) , ` therefore `h_0 -h = l (cos alpha_(0) - cosalpha_0)`
Substituting into the EXPRESSION for the tension of the thread we obtain
`T = mg (3 cos alpha - 2 cos alpha_0)`


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