Mastering Physics wk5

Mastering Physics wk5

6/7/2015 MasteringPhysics: Assignment Week5 https://session.masteringphysics.com/myct/itemView?view=print&assignmentProblemID=48433354 1/3 Item 9 Learning Goal: To understand the vector nature of momentum in the case in which two objects collide and stick together. In this problem we will consider a collision of two moving objects such that after the collision, the objects stick together and travel off as a single unit. The collision is therefore completely inelastic. You have probably learned that “momentum is conserved” in an inelastic collision. But how does this fact help you to solve collision problems? The following questions should help you to clarify the meaning and implications of the statement “momentum is conserved.” Part A What physical quantities are conserved in this collision? ANSWER: Part B Two cars of equal mass collide inelastically and stick together after the collision. Before the collision, their speeds are and . What is the speed of the two­car system after the collision? You did not open hints for this part. ANSWER: the magnitude of the momentum only the net momentum (considered as a vector) only the momentum of each object considered individually v1 v2 6/7/2015 MasteringPhysics: Assignment Week5 https://session.masteringphysics.com/myct/itemView?view=print&assignmentProblemID=48433354 2/3 Part C Two cars collide inelastically and stick together after the collision. Before the collision, the magnitudes of their momenta are and . After the collision, what is the magnitude of their combined momentum? You did not open hints for this part. ANSWER: Part D Two cars collide inelastically and stick together after the collision. Before the collision, their momenta are and . After the collision, their combined The answer depends on the directions in which the cars were moving before the collision. v1 + v2 v1 − v2 v2 − v1 v1 v2 −−−− √ v1+v2 2 v1 2 + v2 √ −−−−−−−2 p1 p2 The answer depends on the directions in which the cars were moving before the collision. p1 + p2 p1 − p2 p2 − p1 p1p2 −−−− √ p1+p2 2 p1 2 + p2 √ −−−−−−−2 p⃗1 p⃗2 ⃗ 6/7/2015 MasteringPhysics: Assignment Week5 https://session.masteringphysics.com/myct/itemView?view=print&assignmentProblemID=48433354 3/3 momentum is . Of what can one be certain? You did not open hints for this part. ANSWER: Part E Two cars collide inelastically and stick together after the collision. Before the collision, the magnitudes of their momenta are and . After the collision, the magnitude of their combined momentum is . Of what can one be certain? You did not open hints for this part. ANSWER: p⃗ p⃗= p1 + → p2 → p⃗= p1 − → p2 → p⃗= p2 − → p1 → p1 p2 p p1 + p2 ≥ p ≥ p1p2 −−−− √ p1 +p2 ≥p ≥ p1+p2 2 p + ≥ p ≥ | − | 1 p2 p1 p2 p1 + p2 ≥ p ≥ p1 2 + p2 √ −−−−−−−2

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