Space Time & Motion A.2 Forces & Momentum (id: f69b0e371)

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 mass Y attached to a rope is moving in uniform circular motion on a frictionless table as shown on the diagram. The circular path of constant radius r is shown with the dotted line. The mass X is hanging from the lower end of the rope.

The masses of X and Y can be adjusted. What independent adjustments to mass X and mass Y could produce uniform circular motion at a lower speed v, but with the same radius r?

A. mass X:increase; mass Y:increase
B. mass X:decrease; mass Y:increase
C. mass X:increase; mass Y:decrease
D. mass X:decrease; mass Y:decrease


参考答案:  C


本题详细解析:

$\underline{\text{Explanation}}$: 
Centripetal force is provided by the weight of the hanging mass $X$, therefore

• $Xg=\frac{Y{v}^2}{r}$

To maintain the same radius with a decrease in $v$, this equation should hold. When the linear speed decreases, therefore to keep the equation balanced, the mass $Y$ should increase, or $X$ should decrease.

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