The rollers on the sides of the block keep it from moving ho
     The rollers on the sides of the block keep it from moving horizontally. The pins that the rollers rotate on are frictionless. The coefficient of friction between all rollers and the block is 0.6.  What is the direction of the force exerted by the roller on the lower surface of the block?   
  
  Solution
there can not be any horizontal force on block by rolar because same force will act on rolar in opposit direction that will disturb the equilibrium.. and rolar will start rotating
so
B is the answer

