Space Time & Motion A.2 Forces & Momentum (id: d03e59748)

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 piece of metal of weight W is suspended by two id. nz)*,1qluh k5b .fwtwj)ycne5e1rco2 p(wuy6 brk )wntical strings. Each string pasoyc2u rb6e(pw5k r)1wses through a pulley and is attached to a block of mass m. The system is in equilibrium

What must be true for m such that the two strings attached to the piece of metal are almost horizontal?

A. $m< \frac{w}{g}$
B. $\frac{w}{2g} < m < \frac{w}{g}$
C. $m > \frac{w}{g}$
D. $m < \frac{w}{2g}$


参考答案:  C


本题详细解析:

$\underline{\text{xplanation}}$: 
For a string to be almost horizontal, the angle of inclination of the string $\theta$ will be very small

 $\text{[Created with Chemix (https://chemix.org)]}$

The piece of metal is stationary, so $W=2Tsin\theta$
For very small inclination angle $\theta$, $sin\theta$ will be very small 
For the above equation to be valid; the value of the tension T in the string must be very high. T >> W

$T=mg$

Which means that the mass of the block must be higher than the mass of the metal. So $m>\frac{W}{g}$

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