Can the kinetic energy of an object be negative? Can the potential energy be negative?

$A$ rifle bullet loses $\left(\frac{1}{20}\right)^{th}$ of its velocity in passing through a plank. Assuming that the plank exerts a constant retarding force, the least number of such planks required just to stop the bullet is .............

In a perfectly inelastic collision, two spheres made of the same material with masses $15 \ kg$ and $25 \ kg$, moving in opposite directions with speeds of $10 \ m/s$ and $30 \ m/s$, respectively, strike each other and stick together. The rise in temperature (in $^{\circ}C$), if all the heat produced during the collision is retained by these spheres, is: (specific heat of sphere material $31 \ cal/kg \cdot ^{\circ}C$ and $1 \ cal = 4.2 \ J$)

$A$ body of mass $4 \,kg$ is moving with momentum of $8 \,kg \,m/s$. $A$ force of $0.2 \,N$ acts on it in the direction of motion of the body for $10 \,s$. The increase in kinetic energy in joules is

Given below are two statements:
Statement $I$: $A$ truck and a car moving with the same kinetic energy are brought to rest by applying brakes which provide equal retarding forces. Both come to rest in equal distance.
Statement $II$: $A$ car moving towards the east takes a turn and moves towards the north, the speed remains unchanged. The acceleration of the car is zero.
In the light of the given statements, choose the most appropriate answer from the options given below.

$A$ particle $P$ is sliding down a frictionless hemispherical bowl. It passes the point $A$ at $t = 0$. At this instant of time, the horizontal component of its velocity is $v$. $A$ bead $Q$ of the same mass as $P$ is ejected from $A$ at $t = 0$ along the horizontal string $AB$ (see figure) with the speed $v$. Friction between the bead and the string may be neglected. Let ${t_P}$ and ${t_Q}$ be the respective time taken by $P$ and $Q$ to reach the point $B$. Then