Q1: On a ladder resisting on a smooth ground and leaning against a rough vertical wall, the force of friction acts

ANS:C - upwards at its upper end

"upwards at its upper end" refers to a hypothetical situation where the upper end of the ladder experiences an upward frictional force. In the scenario described, a ladder is leaning against a rough vertical wall and resisting on a smooth ground. The force of friction primarily prevents the ladder from slipping or sliding either horizontally or vertically. In reality, the force of friction doesn't act upwards at the upper end of the ladder. Friction opposes relative motion between surfaces in contact, and in this case, it acts horizontally to prevent the ladder from slipping away from the wall. Therefore, the concept of a frictional force acting upwards at the upper end of the ladder is not applicable to the described scenario. It contradicts the physical understanding of friction and its role in preventing slipping or sliding.