本题目来源于试卷: Space Time & Motion A.2 Forces & Momentum，类别为 IB物理学
[单选题]
A car of mass $m$ and a truck of mass $3 \, m$ travelling in opposite directions collide and stick together. The speeds of the car and the truck just before the crash are $2 \, v$ and $v$ respectively. What is their speed after the collision?
A. $\frac{1}{4}v$
B. $\frac{4}{5}v$
C. $\frac{5}{4}v$
D. $4 \, v$
参考答案: A
本题详细解析:
Explantion:
The vehicles move in oppsite directio2q(o urc*vuoww1n jzlh /0(4 8qz +z *th)jeawns. Therefore the total momentum before the collision is
u(zz+2o ha0j j(8 lq*h1z)w onr 4/cwuwt*eqv $m(2v)+(-3)v=-mv$
By the principle of conservation of momenntum, the momentum of the vehicles after the collision is equal to the total momentum before the collision.
$-mv=(m+3m)v_t$
Where $v_f$ is the velocity of the vehicles after the collisions
$v_f$=$\frac {-mv} {4m}$
$v_f$=$\frac {-v} {4}$
Therfore the speed is $\frac {1} {4}$ $v$
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