# Talk

## Maths question

(10 Posts)
Leanne198428 Tue 13-Feb-18 19:38:25

Go can some help me?? A speed camera picked me up speeding. I was doing 70mph in a variable speed limit on M4. Im not aguing my points however I may lose my job as it was a works car and being caught 20mph over is gross misconduct. I have asked for the camera tolerance and recieved this Information. Accuracy +1.0m/-5.0m and +/- 100ms. What would this give me +/- MPH if I was travelling at 70mph? Is it possible I was below the 70mph and therefore under the 20mph for gross misconduct? Please help!

TellsEveryoneRealFacts Tue 13-Feb-18 19:40:01

what was the speed limit at the time and what speed were you doing?

MongerTruffle Tue 13-Feb-18 19:41:44

what was the speed limit at the time and what speed were you doing?
Presumably it was 50mph and the OP has said that she was doing 70mph.
Why post this in Homework Corner, OP?

MongerTruffle Tue 13-Feb-18 19:44:47

+1.0m/-5.0m
Is that miles or metres (or something else)?

Leanne198428 Tue 13-Feb-18 19:51:52

It was +1.0m - 5.0m

Leanne198428 Tue 13-Feb-18 19:52:13

Meters

Leanne198428 Tue 13-Feb-18 20:03:16

Meters

TeenTimesTwo Wed 21-Feb-18 13:42:22

You need to know the distance they measured you over

70 miles per hour = 31.2928 metres/second. (according to google)

If they measure you over distance x metres. And you took y time.

They have got

x/y = 31.2928

To get the smallest answer you want x to be smaller and y to be larger.

The distance could have been shorter by 5 metre and the time longer by 100ms

Actual speed could have been (x-5)/(y+0.1)

if distance was 100m, time would have been 3.195 seconds
So with their tolerance your speed could have been 28.83m/sec (64.49mph)

If distance was 1000m time would have been 31.95 seconds
So with their tolerance your speed would have been 31.04m.sec (69.43mph)

The bottom line is that if they have said you were exactly at 70mph, then whatever distance they measured over, given they say there is tolerance in both the distance and the time you could have been under by a little bit.

hope this helps.

If x is 100m then y is

TeenTimesTwo Wed 21-Feb-18 13:45:46

From the distance tolerance I am thinking this was an 'average speed' camera over a considerable distance rather than an instant speed one. Otherwise I don't see how the distance tolerance could be as much as 5m less.

Leanne198428 Wed 21-Feb-18 14:11:57

This is actually a fixed MIDAS unit on the M4. It is not average Speed?

Your help is greatly appreciated. I know the white lines are 2m apart so I will count the number of them tonight giving me the distance.