$A$ small block of mass $m$ slides along a smooth track as shown in the figure. If it starts from rest at point $P$,what is the velocity of the block at point $Q$?

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

$A$ bullet of mass $0.04\; kg$ moving with a speed of $90\; m/s$ enters a heavy wooden block and is stopped after a distance of $60\; cm$. What is the average resistive force exerted by the block on the bullet (in $; N$)?

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?

The total work done on a particle is equal to the change in its kinetic energy. This is applicable:

$A$ mass $m$ slips along the wall of a semispherical surface of radius $R$. The velocity at the bottom of the surface is