M- v/2 Figure P6.64

The conservation of momentum tellsus that the momentum of a system ofinteracting particles must remain constant ifthere are no outside forces. However, whentwo cars collide head-on, they can almostinstantly come to rest (and crumpleunfortunately). This system is essentiallyisolated since the only important interactionsare between the two cars. How can youreconcile these two observations?

Rock A of mass M and another rock B of mass 2M are released from a height h above the ground. Upon impact which relationship correctly states the momenta of rocks A and B?

A pendulum consists of a smallobject called a bob hanging froma light cord of fixed length, withthe top end of the cord fixed, asrepresented in Figure CQ7.5. Thebob moves without friction, swingingequally high on both sides. Itmoves from its turning point Athrough point B and reaches itsmaximum speed at point C. (a) Atwhat point does the bob have nonzeroradial acceleration and zero tangential acceleration?What is the direction of its total acceleration at this point?(b) At what point does the bob have nonzero tangentialacceleration and zero radial acceleration? What is thedirection of its total acceleration at this point? (c) At whatpoint does the bob have both nonzero tangential and radialacceleration? What is the direction of its total accelerationat this point?