Question

Why we cant open and close a door by appyling force at hinges?

Answer 1

we can't open or close a door while applying force at hinges because for closing and opening of door the door performs a rational motion at its hinges. It moves when there is a net moment in that direction. The formula for moment of force is the magnitude of force multiplied by the perpendicular distance from the force to the pivot. In this case the hinges are the pivot, thus application of force of hinges makes the perpendicular distance 0. Giving a 0 moment of force. hence v can not close or open a door by applying force on the hinges

Answer 2

Because the torque of force at the hinges is zero as perpendicular distance is zero . Hence there is no rotational motion