Brakes stop a train in a distance $x$. If the braking force is reduced to one-fourth of its original value,what distance will the train travel before coming to a stop?

Select the incorrect statement regarding the mechanical energy of a body/system.

$A$ block of mass $m$ is suspended vertically from an elastic string with a force constant $k = mg/a$. Initially,the string is at its natural length and the block is allowed to fall freely. What will be its kinetic energy when the block passes through the equilibrium position?

$A$ ball bounces to $80\%$ of its original height. What fraction of its mechanical energy is lost in each bounce?

$A$ body moves from rest with a constant acceleration. Which one of the following graphs represents the variation of its kinetic energy $K$ with the distance travelled $x$?

$A$ particle which is experiencing a force,given by $\vec F = 3\hat i - 12\hat j$,undergoes a displacement of $\vec d = 4\hat i$. If the particle had a kinetic energy of $3\, J$ at the beginning of the displacement,what is its kinetic energy (in $J$) at the end of the displacement?