Space Time & Motion A.2 Forces & Momentum (id: a62699c16)

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 firecracker is at rest just befbuci.d.6yw e9ep+e0(2t bl: xm(anctore expl9lgl33 sx i2geoxau ao43b:j-oding. Upon exploding, the firecracker splits into two unequal parts which are projecta94oaisl u:oxgb-2le33 3 jxged in exactly opposite directions. Which of the following must be true?

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A. The total kinetic energy of the firecracker remains unchanged before and after the explosion.
B. The kinetic energy of the two parts after the explosion is identical.
C. The total momentum of the firecracker is unchanged after the explosion.
D. The velocities of the two parts are exactly equal in magnitude but opposite in direction.


参考答案:  C


本题详细解析:

$\underline{\text{Explanation}}$: 
A. Incorrect because $E_k$ changed from zero to non-zero because the chemical potential energy in the firecracker is converted into kinetic energy which is divided between the two parts after the explosion.

B. Incorrect; Because $E_k=({\displaystyle \frac{p^2}{2m}})$ and the momenta must be equal, the kinetic energies must be unequal as the masses are not equal.

C. Correct; Momentum is always conserved in any process for an isolated system.

D. Incorrect because since momentum is conserved, unequal parts must have unequal velocities.

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