A 3kg ball at 18m/s collides elastically with a stationary 9kg ball. What is the speed of the 3kg ball after collision?
For elastic collision, momentum and kinetic energy conserved: m1v1+m2v2=m1v1'+m2v2' and ½m1v1²+... per NCERT. Solving gives velocities matching 9 m/s. Inelastic loses energy. So option B is correct.
Ref: NCERT Class 11 Physics > Chapter 6: Work, Energy and Power > Topic: Work, Energy and Power - Work-Energy Theorem