What is the angle between frictional force and instantaneous velocity of the body moving over a rough surface ?

What is the difference between average velocity and instantaneous velocity?

Frictional force between two bodies

In a situation the contact force by a rough horizontal surface on a body placed on it has constant magnitude. If the angle between this force and the vertical is decreased, the frictional force between the surface and the body will

What is the direction of frictional force actiog on a body moving or sliding towards east ?

A horizontal surface is partly smooth and partly rough. A particle is projected along the smooth part with speed u. After travelong a distance d, to rest. If mu is the coefficient of friction between particle and surface, the distance moved over the rough surface is:

Limiting value of static frictional force on a block placed on the rough surface depends on