The speed limit is 25 miles per hour, but it seems that many of the cars are going faster. the city places 2 counter strips 360 feet apart in the lane closest to the school. a teacher times one car's front tires crossing the strips in the 7.0 sec. is the car speeding? how do you solve this?

You figure out how long it would take a car traveling at 25 mph
to cover 360 ft.  Any driver who does it in less time is speeding.

           (25 mi/hr) · (5,280 ft/mile) · (1 hr / 3,600 sec)

       =    (25 · 5280 / 3600)  ft/sec  =  (36 and 2/3) feet per second.

To cover 360 ft at 25 mph, it would take

                360 ft / (36 and 2/3 ft/sec)  =   9.82 seconds .

Anybody who covers the 360 feet in less than 9.82 seconds
is moving faster than 25 mph.


If you're interested, here's how to do it in the other direction:

Let's say a car covers the 360 feet in ' S ' seconds.
What's the speed of the car ?

           (360 ft / S sec) · (1 mile / 5280 feet) · (3600 sec/hour)

       =    (360 · 3600) / (S · 5280)  mile/hour

       =        245.5 / S    miles per hour .

The teacher timed one car crossing both strips in 7.0 seconds.
How fast was that car traveling ?

                   245.5 / 7.0  =  35.1 miles per hour

Another teacher timed another car that took 9.82 seconds to cross
both strips.  How fast was this car traveling ?

                        245.5 / 9.82  =  25 miles per hour