Question

a reel of massless thread unrolls itself falling down under gravity the acceleration of its fall is: options: g,2/3g,g/2,4/5g. please solved answer

Answer 1

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Answer 2

Given :

Mass of the disk = M

To Find :

The acceleration due to gravity of its fall = ?

Solution :

• Let T be the tension in the thread and I be the moment of inertia of the disc

• We have the relation, Net torque = I×Angular acceleration

            $T\times R=I\times \alpha$

            $T\times R=\frac{MR^{2} }{2}\times \frac{a}{R}$

            $T = \frac{Ma}{2}$

• By equating forces

          $Mg-T=Ma$

          $Mg-\frac{Ma}{2} =Ma$

          $Mg=\frac{3Ma}{2}$

           $a=\frac{2g}{3}$        

The acceleration due to gravity of its fall is 2g/3