A bullet is fired from a rifle. If the rifle recoils freely, then the kinetic energy of the rifle is

If a body looses half of its velocity on penetrating $3 \,cm$ in a wooden block, then how much will it penetrate more before coming to rest ........... $cm$

A bomb of mass $3.0\, Kg$ explodes in air into two pieces of masses $2.0 \,kg$ and $1.0\, kg$. The smaller mass goes at a speed of $80 m/s$.The total energy imparted to the two fragments is ............. $kJ$

An object of mass ' $m$ ' initially at rest on a smooth horizontal plane starts moving under the action of force $F=2 N$. In the process of its linear motion, the angle $\theta$ (as shown in figure) between the direction of force and horizontal varies as $\theta= kx$, where $k$ is a constant and $x$ is the distance covered by the object from its initial position. The expression of kinetic energy of the object will be $E =\frac{ n }{ k } \sin \theta$. The value of $n$ is $.....$

An electron and a proton are detected in a cosmic ray experiment, the first with kinetic energy $10\; keV$, and the second with $100\; keV$. Which is faster, the electron or the proton? Obtain the ratio of their speeds. (electron mass $=9.11 \times 10^{31}\; kg$. proton mass $=1.67 \times 10^{-27}\;$$ kg , 1 \;eV =1.60 \times 10^{-19} \;J )$

A particle of mass $m$ at rest is acted upon by a force $F$ for a time $t$. Its Kinetic energy after an interval $t$ is