Space Time & Motion A.2 Forces & Momentum (id: 55ecc3290)

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 point P is subjected to three simultaneous forces of magnitudes $F_A$>$F_B$>$F_C$ $F_A$>$F_B$>$F_C$. Point P is in equilibrium. Which of the following statements is not always true about the magnitudes of the forces?
I.$F_A$=$F_B$+$F_C$
II.$F_A$≤$F_B+F_C$
III.$F_A$＞$F_B$-$F_C$

A. I only
B. I and II only
C. I and III only
D. II and III only


参考答案:  A


本题详细解析:
$\underline{\text{Explanation}}$: 
Vectors of forces in equilibrium form a triangle or a straight line. 
The sum of two sides of a triangle is always greater than the third (II is always true). The difference between two sides of a triangle is always less than the third (III is also always true). 
I is true only when the three forces are in a straight line and $F_B$$F_C$$F_A$$F_A$ (not always true, as required by the question).

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