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Pairs of markings a set distance apart are made on highways so that police can detect drivers exceeding the speed limit. Over a fixed​ distance, the speed R varies inversely with the time T. In one particular pair of​ markings, R 58 is mph when T is 7 seconds. Find the speed of a car that travels the given distance in 9 seconds.

Answer :

Answer: [tex]45.11\ mph[/tex]

Step-by-step explanation:

Given

Speed R varies inversely with time T i.e.

[tex]R\propto \dfrac{1}{T}\\\\R=\dfrac{C}{T}\quad [\text{C=constant}][/tex]

when R=58 mph, T=7 s i.e.

[tex]58=\dfrac{C}{7}\quad \ldots(i)[/tex]

when T=9 s

[tex]R=\dfrac{C}{7}\quad \ldots(ii)[/tex]

Divide (i) and (ii)

[tex]\Rightarrow \dfrac{58}{R}=\dfrac{9}{7}\\\\\Rightarrow R=\dfrac{7}{9}\times 58\\\\\Rightarrow R=45.11\ mph[/tex]

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