Force of friction is greater in case of rough surface or smooth surface?

State whether True or False Force of friction is greater in case of smooth surface than rough one.

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

The upper half of an inclined surface is perfectly smooth but the lower half is rough . A body starts sliding down the plane and stops immediately on reaching the bottom. The inclination of the plane is 30^(@) with the horizontal. Show that the frictional resistance of the rough part of the surface is equal to the weight of the body.

In which case will the decreases in the value of the acceleration due to gravity be greater (with respect to that on the earth's surface) -at 1 km above the earth's surface or 1 km below the earth's surface ?

If the force of friction is equal to the force applied, then friction may be