Q27 of 63 Page 114

A block of mass m moves on a horizontal circle against the wall of a cylindrical room of radius R. The floor of the room on which the block moves is smooth but the friction coefficient between the wall and the block is μ. The block is given an initial speed u0. As a function of the speed u write (a) the normal force by the wall on the block, (b) the frictional force by the wall and (c) the tangential acceleration of the block. (d) Integrate the tangential acceleration to obtain the speed of the block after one revolution.


The normal reaction will be balancing the centrifugal force. Hence,



So, the normal reaction will be,


(b)


Friction force is at maximum as the body is moving,



Putting the value of N we get,



This will be the force of friction.


(c)


The only force changing the velocity will be friction. The friction is,




As the tangential acceleration will actually decrease the speed, so,



(d)



So, we can write,







For one complete revolution, s=2∏R. so,




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A table with smooth horizontal surface is fixed in a cabin that rotates with a uniform angular velocity ω in a circular path of radius R (figure 7-E3). A smooth groove AB of length L (<< R) is made on the surface of the table. The groove makes an angle θ with the radius OA of the circle in which the cabin rotates. A small particle is kept at the point A in the groove and is released to move along AB. Find the time taken by the particle to reach the point B.


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A car moving at a speed of 36 km/hr is taking a turn on a circular road of radius 50 m. A small wooden plate is kept on the seat with its plane perpendicular to the radius of the circular road (figure 7-E4). A small block of mass loo g is kept on the seat which rests against the plate. The friction coefficient between the block and the plate is μ = 058. (a) Find the normal contact force exerted by the plate on the block. (b) The plate is slowly turned so that the angle between the normal to the plate and the radius of the road slowly increases. Find the angle at which the block will just start sliding on the plate.