A screw is a modification of an inclined plane . The threads of a screw are like an inclined plane wrapped around a cylinder.

If we raise an one end of plank than we can use it as inclined plane.

The stair case used by the airline passengers is a modified form of inclined plane.

As slope increases component of weight along inclined plane increases so more effort required to push a load up.

Distance between the successive threads of screw is known as Pitch of screw.

A screw is preferred over a nail to insert into wood because it requires lesser force to insert. Therefore the value of force required to insert a screw in the given question is less than 3 N.

A door knob is an example of simple machine.

Gangplank is a flat surface  whose end points are at different heights. So it is an example of inclined plane.

A Wedge is a triangular shaped tool ,and is a portable inclined plane. It can be used to separate two objects or portion of objects.

A crowbar also called a wrecking bar is commonly used to open a nailed wooden crates or pry apart boards.

A wedge can be made by putting two inclined plane together .

(a) Screw has thread like grip on it so it holds more firmly than a nail.

As slope increases component of weight along inclined plane increases so more effort required to push a load up.

$ MA = \displaystyle \frac{L _{car}}{E _{car}} = \frac{EA}{LA}$
$\displaystyle \frac{L _{car}}{400} = \frac{5000}{250}$
$L _{car} = 8000 N$
Fractional change
$= \displaystyle \frac{L _{car}-E}{E}$
$= \displaystyle \frac{8000 - 400}{400}$
$= \displaystyle \frac{7600}{400}$
$=19$

A screw is a modification of an inclined plane . The threads of a screw are like an inclined plane wrapped around a cylinder.

If threads of a screw are closer then inclination decreases so it has became easy to drive screw or effort required will be less.