Which will cause more friction : a rough surface or a smooth surface ? Why ?

To determine the coefficient of friction between a rough surface and a block, the surface is kept inclined at 45^(@) and the block is released from rest. The block takes a time t in moving a distance d. The rough surface is then replaced by a smooth surface and the same experiment is repeated. The block now takes a time t/2 in moving down the same distance d. The coefficient of friction is

In the following problems, indicate the correct direction of friction force acting on the cylinder, which is pulled on a rough surface by a constant force F . A cylinder is placed on a rough plank which in turn is placed on a smooth surface. The plank is pulled with a constant force F . The friction force can be given by which of the following diagrams. .

Smooth surface produces _____ friction than a rough surface.

A block weighing 10 N tavels down a smooth curved track AB joined to a rough horizontal surface. The rough surface has a friction coeficient of 0.20 with the block. If the block starts slipping on the track from a point 1.0 m above the horizontal surace, how far will it move on the rough surface?

A block weighing 40N travels down a smooth fixed curved track AB joined to a rough horizontal surface (figure). The rough surface has a friction coefficient of 0.10 with the block. If the block starts slipping on the track from a point 2.0m above the horizontal surface, the distance it will move on the rough surface is :-

A wet surface offers less/more friction than a dry surface.