calculating time given speed and distance

Ive been running TSD rallys for a while now and I have never been able to get the math to work out to calculate a time given a target speed and a delta mileage.

i.e.: 34mph (covering a distance of) .65 miles = X.XX minutes

I have tried and i can’t get the math to work out (damn standard units on top of time conversions) and a conversion to metric induces further errors. I have tried using unit conversion and using 60mph over 1.000 mile = 1.00 minutes, 30mph -> 2.00 minutes, 120 -> 0.50 minutes and I can’t get the math to check out.

Scoring is done based on minutes w/ a decimal (minutes and tenths/hundredths/thousandths of a minute) and we need a human readable minutes:seconds time. Any help doing that would be nice too.

I am severely humbled to ask all this, having scored well in high school physics, aced a similar college phyiscs course, and slept thru and aced a conceptual physics course. I should know how to do this and I can’t.

Distance = rate * time, so time = distance/rate.

t = 0.65 mi/34 mi/hr = 0.019 hours * 60 min/hour = 1.147 minutes.

Isn’t it like this? I don’t know what exactly you are asking for because this seems all too easy.

speed = distance over time

or

v = d / t

with the example you give, we have miles and hours. but we want the time to be in minutes.

So t = d / v

t = .65 miles / 34 mph
t = .019117647 hours

convert to minutes by doing this.

t = .019117647hrs * 60minutes/1hr
t = 1.147058824minutes

we want the decimal chunk to be in seconds

so the 0.147058824 is multiplied by 60 seconds per 1 minute.

which gives a readable time of:

1 minute and 8.8235 seconds or rounded nicely would give

00:01:09

hr:min:sec

or 00:01:08:82 since you might want the milliseconds.

Where does metric come into this? Are you thinking that minutes/tenths/hundredths is metric? Don’t you mean decimal?

The only conversions you need are to be sure you are working in all hours or all minutes, just don’t mix em. Then think of this basic equation:

RATE = DISTANCE / TIME

If you decide to work in minutes instead of hours, then we have:

(34 MPH / 60 mins per hour) = .65 miles / T minutes

or:

34 .65
---- = ----
60 T

cross-multiply & solve for T:

34T = .65 * 60

T = 39 /34

T = 1.1470588 minutes

Does that answer your question?

I was afraid that would happen with proportional spacing. I could have used the code tag to unscramble the jumble:



34      .65
---  =  ----
60       T


As long as you don’t mix units, all you really need are these three equations, which of course are derived from each other. Pick the one that takes the fewest steps to get to the solution:

RATE = DISTANCE / TIME

TIME = DISTANCE / RATE

DISTANCE = TIME * RATE

Oh, and if you have a SHARP EL-546G scientific calculator handy. (I think any SHARP EL-500 Series should be able to do this) After finding out the time in hours, using the t = d / v formula, and noting that miles will divide out and hours will remain…

You can just use the hours decimal of

0.019117647

and press the Degree,Minute,Seconds button

or D°M’S button located at the fourth row and third column.

This button will convert any number in decimal form into degrees (or hours), minutes and seconds, with 2 places for the milliseconds spot.

so you end up with 0°01’08.82 on the display of the calculator.

If you don’t have a scientific calculator that can do this function just stick with my previous post’s method and all should be fine.

bah I don’t know why I keep calling those 2 extra spots after the seconds’ place milliseconds. They should be called deciseconds and centiseconds.

Oh well I hope we helped.

Yep that helped. What kept killing me was either the conversion from MPH to miles/minute or from .00xx hours to minutes.

The metric reference was because in school I deal exclusively with metric. Given standard units the first thing is to convert them to metric.

Here is what I call an “Ultra Calculator” from my website.
http://www.1728.com/velocity.htm
It deals with velocity, time and distance. You can input each of these three variables from dropdown menus offering twelve units each.
example: you can enter velocity in
cm/sec;
feet/minute;
feet per second;
inches per second;
km per hour;
kilometers per second;
knots;
metes per second;
miles per hour;
miles per minute;
miles per second; and
millimeters per second.

Basically enter any 2 of the 3 quantities and you’ll get the third (also calculated in a list of 12 units).

Also, you migt find this velocity converter handy to use:
http://www.1728.com/convvel.htm

Any small airport can give you a flighttime calculator. You read instructions, rotate distance to speed, look at time. It is a slide rule thingie, but that was how I learned. No calculators in my schools.

Or, 60miles per hour for sixty minutes = 60 miles…Do not change your units. Or change your units to this and then change the result to your liking. The units rule the equation. The equation rules under earlier postings.