The kinetic energy $K$ of a particle moving along the $x$-axis varies with its position $x$ as shown in the figure. The magnitude of the force acting on the particle at $x = 9 \ m$ is $.... \ N$.

What is a variable force? Write the equation for the work done by a variable force in one dimension.

When a rubber band is stretched by a distance $x$,it exerts a restoring force $F = ax + bx^2$,where $a$ and $b$ are constants. The work done in stretching the rubber band by a distance $L$ from its unstretched position is:

$A$ force $F$ acting on an object varies with distance $x$ as shown in the graph. The force is in $N$ and $x$ is in $m$. The work done by the force in moving the object from $x = 0$ to $x = 6$ is ............. $J$.

$A$ particle moves under the effect of a force $F = Cx$ from $x = 0$ to $x = x_1$. The work done in the process is

Arrange the four graphs in descending order of total work done; where $W_{1}, W_{2}, W_{3}$ and $W_{4}$ are the work done corresponding to Figure-$a$,Figure-$b$,Figure-$c$ and Figure-$d$ respectively.