Rotation 3 Question 23

29. A man pushes a cylinder of mass m1 with the help of a plank of mass m2 as shown. There is no slipping at any contact. The horizontal component of the force applied by the man is F. Find

(1999,10M)

(a) the accelerations of the plank and the centre of mass of the cylinder and

(b) the magnitudes and directions of frictional forces at contact points.

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Solution:

  1. We can choose any arbitrary directions of frictional forces at different contacts.

In the final answer the negative values will show the opposite directions.

Let f1= friction between plank and cylinder

f2= friction between cylinder and ground

a1= acceleration of plank

a2= acceleration of centre of mass of cylinder

and α= angular acceleration of cylinder about its CM.

Since, there is no slipping anywhere

a1=2a2

a1=Ff1m2

a2=f1+f2m1

α=(f1f2)RI=(f1f2)R12m1R2

α=2(f1f2)m1R

a2=Rα=2(f1f2)m1

(a) Solving Eqs. (i) to (v), we get

(b)

a1=8F3m1+8m2 and a2=4F3m1+8m2f1=3m1F3m1+8m2;f2=m1F3m1+8m2

Since, all quantities are positive, they are correctly shown in figures.



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