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General
Easy

Question

A wooden block with mass 2 m is attached to the shaft of an electric motor mounted on a plank free to move on the floor. The mass of the plank and motor is m. The initial seperation between the block and motor is l. When the motor is switched on, block moving with acceleration a. If mu is the coefficient of friction time after which the two bodies collide is

  1. square root of fraction numerator 2 l over denominator mu g end fraction end root    
  2. square root of fraction numerator 2 l over denominator 2 mu g plus a end fraction end root    
  3. square root of fraction numerator 2 l over denominator mu g plus 3 a end fraction end root    
  4. square root of fraction numerator 2 l over denominator a minus 2 mu g end fraction end root    

The correct answer is: square root of fraction numerator 2 l over denominator a minus 2 mu g end fraction end root

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