Show that internal forces can change the kinetic energybut not linear

1.	Show that internal forces can change the kinetic energybut not linear momentum .
Answer» Solution :`vecF_("ext") = M veca_(CM) implies vecF_("ext") = (M d vecv_(CM))/(dt)` `vecF_("ext") = (d)/(dt) (M vecv_(CM))` Only external forces can change the MOMENTUM of a SYSTEM . Internal forces can gives rise to kinetic energy . A compressed SPRING attached to two blocks , converts its potential energy into kinetic energy . This K.E. is due to internal forces .

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