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Units and Measurement
Question
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Electron and proton at rest are released. What is the velocity of centre of mass when the two approach towards each other?

Answer

When an electron and proton at rest are released, the velocity of the centre of mass is zero, when the two approach towards each other. This is because, in the absence of external force, the centre of mass moves with constant velocity.

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Some More Questions From Units and Measurement Chapter

Define unit.

What are the two main required characteristics of a unit?

Can we use same units for different physical quantities?

Can we use different units to measure same physical quantity?

To measure a physical quantity X, the unit U is repeatedly used for n times. What is the magnitude of physical quantity?

Does the numerical factor in the quantitative measurement depend on the system of unit used?

Is one unit sufficient to measure a physical quantity?

Can a physical quantity have two or more units? Give example.

What are fundamental quantities?