A wagon weighing $1000\, kg$ is moving with a velocity $50\,km/h$ on smooth horizontal rails. A mass of $250 \,kg$ is dropped into it. The velocity with which it moves now is ......... $km/hour$

A body is moving with a velocity $v$, breaks up into two equal parts. One of the part retraces back with velocity $v$. Then the velocity of the other part is

A shell, in flight, explodes into four unequal parts. Which of the following is conserved?

A shell of mass $m$ is at rest initially. It explodes into three fragments having mass in the ratio $2: 2: 1$. If the fragments having equal mass fly off along mutually perpendicular directions with speed $v$, the speed of the third (lighter) fragment is :

A man is standing at the centre of frictionless pond of ice. How can he get himself to the shore

A man (mass $= 50\, kg$) and his son (mass $= 20\, kg$) are standing on a frictionless surface facing each other. The man pushes his son so that he starts moving at a speed of $0.70\, ms^{-1}$ with respect to the man. The speed of the man with respect to the surface is ........ $ms^{-1}$