Question

What will be the position of the normal force, when the object is about to topple?
A. Normal force will be acting along the centre of gravity.
B. Normal force will be acting at distance x decided by the mass of the object.
C. Normal force will be acting at the edge of the body, farther from the point of application of the force.
D. Normal force will be acting at the edge of the body, nearer from the point of application of the force.

Answer 1

The normal force is a force perpendicular to the surface of contact that opposes the downward force of the weight of the object. When an object is about to topple the normal force will be acting along the centre of gravity. Using this information, we can find out the correct answer.

Complete answer:
The static frictional force and the applied force together will shift the normal force towards the edge of the block, and contribute for a positive torque. There will be no opposite torque acting on the object when the normal force acts along the centre of gravity and the object will start rotating irrespective of its geometry, even when a small force is applied.
The normal force is a force of contact. When two surfaces are not in connection, a normal force can not be exerted on one another. For example, consider a table and a container, when they are not in contact it is not possible to exert normal force on one another. But, when two objects are touching one another, they exert normal force on one another vertical to the contacting surface. Here normal denotes a perpendicular.

Hence option C is the correct answer.

Note: A normal force always holds up the block, but if it is tipping (or nearly tipping), then only the corner of the object can be supporting the weight. So, an object will topple over if its centre of gravity is 'outside' the base, or edge, on which it balances. An object with a wide base, a low centre of gravity is the most stable.