本题目来源于试卷: 2007美国US F=MA物理竞赛，类别为 美国F=MA物理竞赛
[单选题]
A particle moves along the .y n/7 .lbp*kvdb--wl lcpy(wx-axis. It collides ela iz 9b:zww , ,t :op5lsge+*bfostically head-on with an identical particle initially at rest. Which of the following graphs could illustrate t iez:sw5 ,g of*o9w:z ptlb +b,he momentum of each particle as a function of time? 
A.
B.
C.
D.
E.
参考答案: D
本题详细解析:
In a one-dimensional, elastic collision between two identical i;ff+w- og-vp b(2oczmasses (particle 1 and particle 2), where particle 2 is initially at rest, the particles "swap" velocities.
This means partizp cbg;+o-o-(wi 2v ffcle 1, which had initial momentum $p_1$, comes to a complete stop ($p_{1,f} = 0$).
Particle 2, which had initial momentum $p_2=0$, moves off with particle 1's initial momentum ($p_{2,f} = p_1$).
Graph (d) illustrates this perfectly: one particle's momentum drops from a positive value to zero, while the other's momentum jumps from zero to that same positive value.
Total momentum is conserved at all times.
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