Question

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 1

Answer:
`45.11\ mph`

Explanation:

Given

Speed R varies inversely with time T i.e.

`R\propto (1)/(T)\\\\R=(C)/(T)\quad [\text{C=constant}]`

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

`58=(C)/(7)\quad \ldots(i)`

when T=9 s

`R=(C)/(7)\quad \ldots(ii)`

Divide (i) and (ii)

`\Rightarrow (58)/(R)=(9)/(7)\\\\\Rightarrow R=(7)/(9)* 58\\\\\Rightarrow R=45.11\ mph`