Can someone check my work on this problem?
I'd like to be able to figure out how fast cars are going by measure the time it takes to pass me, or for me to pass them. I figure, counting the seconds it takes for one car to pass the other will give me the relative velocity and then I can just add or subtract that from my velocity (assuming all speeds are constant).
Here are my calculations:
Say 1 car length = 13.5 ft
Call the number of seconds it takes for the car to pass me $x$
Then their relative speed is $\frac{13.5 \ ft}{x \ sec} (\frac{1 mi}{5280 ft})(\frac{60 \ sec}{1 \ hr}) = \frac{.1534}{x}$mph.
Now suppose my speed is y mph. Then their "absolute speed" is (y + $\frac{.1534}{x}$)mph.
Are my calculations correct? Something seems wrong here.
Best Answer
There are 3600 seconds in an hour, not 60. You should get $y + \frac{9.20455}{x}\mathrm{ mph}$