A block moving horizontally on a smooth surface with a speed of 20 m/s bursts into two equal parts continuing in the same direction. If one of the parts moves at 30 m/s, with what speed does the second part move and what is the fractional change in the kinetic energy?

Explanation

There is no external force on the block. Internal forces break the block in two parts. The linear momentum of the block before the break should therefore be equal to the linear momentum of the wo parts after the break. As all thevelocities are in same directin we get
`M(20 m/s)=M/2(30m/s)+M/2v`
where v is th speed of the other part. From this equation `v=10m/s.` The change in kinetic energy is `1/2M/2(3m/s)^2+1/2 M/2(10m/s)^2-1/2M(20m/s)^2`
`=m/(450+50-40) m^2/s^2=(50 m^2/s^2)M`.
`Hence the fractioN/Al change in the kinetic energy
`(M(50 m^2/s^2))/(1/2M(20m/s)^2)=1/4`