Question

Why is the tip of an allpin sharp?
A. To increase pressure
B. To decrease pressure
C. Has got nothing to do with pressure
D. To make it light

Answer 1

The all-pin is used for tying up a bundle of sheets together. For this it is needed to penetrate the all-pin into the sheets, with the minimum force possible. By using the definition of pressure, we can relate the force with the sharpness of the all-pin.

Complete answer:
We know that an all-pin is generally used for tying up a set of papers, plastic sheets etc. For this, it is needed to dig a hole inside each of the sheet or paper within which the pin is inserted which holds them together. For that we have to apply the force on a part of the surface area of the sheet or paper on which we are making the hole.
Our effort is a measure of the force applied by us on the surface of the sheet or paper. We want to reduce this effort to make the all-pin easy to use. We know that the force applied on a surface per unit area of contact is known as the pressure. So for a given amount of the force applied by us, if we decrease the area of the all-pin, then the area of contact will decrease. Since the pressure is inversely proportional to the area of contact, so the pressure will increase.
Thus, for increasing the pressure for a given force applied by us to drive the pin inside the sheet or paper, the tip of the all-pin is made sharp.
Hence, the correct option is A.

Note: The sharpness of an all-pin is not only used for reducing our effort for driving the pin inside a sheet or paper, but also for ensuring that the diameter of the hole made is not too large. Our purpose is to tie up the sheets together by using the all-pin, and not to make up the hole in the sheets. So we have to ensure that the sheet does not tear up due to the all-pin.