Answer the following questions (multiple choice):

6, in which of the following situations is the force of friction or friction not involved? a. a hail does not come off the wall. b. when walking we push ourselves by rubbing the sole of the shoe against the grownd. c. primitive man lit a fire. d. the slider on the air track What does the force of friction or friction acting on a sliding block depend on?' a. The type of materials supported their degree of roughness and weight. b. The type of materials supported, their degree of roughness, the weight of the supported block and the supported face (the greater the surface of the face, the greater the friction). c. The type of materials in contact and the weight of the supported body. The frictional foroe acting on a block that is dragged along; a plane has a direction that... a. is perpendicular to the displacement. b. is parallel to the plane. c. depends on the inclination of the force with which it is pulled. The force of friction depends on the speed with: which the sliding body moves. a. True b. Depends on acceleration c. False The friction coefcient represents assigning a number to the drag behavior of... a. the bottom surface, b. the two surfaces and their degree of roughness. c. the upper surface. The coefcient of kinetic friction varies with increasing speed of the dragged body. a. True b. False c. it depends on the lubrication. The force normal to the surface, which is the reaction force against the body of the surface on which it is 3. equal to the weight increased or decreased by the vertical component of the pulling _ force. b, equal to the weight minus the tensile force. c. equal to weight. Weight ls considered a force applied at the center of the body and ha a direcon... a. perpendicular to the ground. b. perpendicular to the inclined plane. c. depends on the angle of the plane