Question 9. A block of wood is placed on a surface. A force is applied parallel to the surface to move the body. The frictional force developed acts (a) normal to the surface upwards (b) normal to the surface downwards (c) along the direction of the applied force (d) opposite to the direction of the applied force Answer
Correct option is B) When we try to slide a body on a surface, the motion of the body is opposed by a force called the force of friction. The frictional force arises due to intermolecular interaction. When an external force (F) is applied to move the body and the body does not move, then the frictional force acts opposite to applied force F and is equal to the applied force i.e., F−f=0 frictional force ,f and applied force F . When the body remains at rest, the frictional force is called the static friction. Static friction is a self-adjusting force. Friction force, f r =μmg Where, μ = coefficient of friction. Hence, friction force act opposite to the direction of motion.
