Space Time & Motion A.2 Forces & Momentum (id: 3c4dcf6df)

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]
An object starts to move in a straightxpylwln )8+ v: linejl7 vdx*4ym3j under the effect of two opposite forces of 12N and 13v4l x*jmjd7y6N


After 5s, the displacement of the object is 25m. What is the mass of the object?

A. 1kg
B. 2kg
C. 3kg
D. 4kg


参考答案:  B


本题详细解析:

$\underline{\text{Explanation}}$:

From the equations of motion, the following expression can be written:

• $s=ut+\frac{1}{2}a{t}^2$

The object starts to move from rest, therefore u=0:

• $25=(\frac{1}{2})(a{)(5)}^2$

• $a=2m{s}^{-2}$

By applying Newton’s Second Law to the object,

$\begin{array}{rl}{\displaystyle F}& {\displaystyle =ma}\\ {\displaystyle 16-12}& {\displaystyle =(m)(2)}\\ {\displaystyle m}& {\displaystyle =2kg}\end{array}$

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