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# What?

A massless string of length $$R$$ is there. It starts doing a vertical motion.

If the length of the purple line is $$R \cos \theta$$, that means the string's length is reduced, but where does it go?

Note by Saraswati Sharma
2 months, 3 weeks ago

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Length of the purpul line will remain R, why should it change to $$R \cos \theta$$? · 2 months, 3 weeks ago

I edited the note . We do vertical motion problem by ignoring Rsin(theta) , yeah I know Rsin(theta) is horizontal component and we are doing "vertical" motion . Calculation of h gives a strong feeling that the string becomes short . · 2 months, 3 weeks ago

The length of the purple line is still R. The length of the red line above h is $$R \cos \theta$$. The total length of the red line and purple line are equal to R. · 2 months, 3 weeks ago