Maths/physics whizzes please

[jellywrestler]

speaking of weedeaters, you ain't seen colourful till you've chased a peacock round a paddock with a weedeater....

[Spuds1234]

The second one is a deflection question, which needs alot more info that what you got. Angle of deflection, pebble mass, and so on.

You could take a rough guess though and say the pebble was 20g and the string was 5g and that all the rotational energy of the plastic string was transferred into the pebble (I doubt it would be though as the string is flexible and the impact would be elastic) which would give you a rough speed that the pebble leaves the string at 80m/s. Obviously this is way to high though as its based off perfect world estimates, but for Oakies needs its probably good enough.

[gunnyrob]

you're over thinking it. Refer to the manufacturers safety info. Most normally specify a distance of about 30 feet. You should be doing a hazard assessment and be acting in accordance with your company safety policy. (Spot the safety auditor)

[The Singing Chef]

Step one: Get weedeater.
Step two: Get 20 - 20g Pebbles of different shapes.
Step three: Play golf.

A fun way to find out? I think so!

[bogan]

Stepping back from the highlighted problem a bit, but why are you guys running a weed eater over pebbles? They do a better job if you use them on weeds!

[Oakie]

Stepping back from the highlighted problem a bit, but why are you guys running a weed eater over pebbles? They do a better job if you use them on weeds!

Used to be just weeds but earthquakes put pebbles, asphalt, crud etc in our green areas.

[Oakie]

you're over thinking it. Refer to the manufacturers safety info. Most normally specify a distance of about 30 feet. You should be doing a hazard assessment and be acting in accordance with your company safety policy. (Spot the safety auditor)

Good point. I guess I am doing a hazard assessment in a round-about way and we will finish up with a policy by default. It's just one of those annoying ones where you'd think everyone will recognise how to keep safe ... but noooo! Silly thing is that even though this is a facility for intellectually disabled adults, it was one of the staff who walked themselves into danger! Seeing the maintenance guy head to foot in PPE wasn't enough of a clue it seems.

[5150]

Is it electric or petrol powered weed eater? If petrol, is it a 4 stroke or a 2 stroke?

Also is it clockwise or anticlockwise spin?

[avgas]

The safe distance is actually a lot smaller than you think. Its to do with the fact that the nylon bends on contact absorbing most of the energy.
So don't be surprise if the actually around 10-20m/s - around a good slingshot speed.

This is why pebbles don't fly a few km's, go through legs of individuals etc after being hit by a weed eater line...............which some of the calculations here would leave you believe (fyi @ 50m/s is tornado speeds......and would blow a pebble through a thin wall).
I almost giggled at the 3-400m/s........that is nearing .22 cal speeds. And those things go for km!

[Oakie]

Is it electric or petrol powered weed eater? If petrol, is it a 4 stroke or a 2 stroke?

Also is it clockwise or anticlockwise spin?

Petrol and 2 stroke I believe. A whole 1.2hp.

[5150]

Petrol and 2 stroke I believe. A whole 1.2hp.

Shit. By my calculations using my FX-82 scientific calculator, she'd be travelling at over mach 4. Oh, hang on, I am holding the calculator up side down.


Ok. Further following a prctical test in my driveway using a Ryobi 2 smoke weed eater and a 10mm round(ish) stone I can confirm that it hit the neighbours shed window from aprox 25 metres away. that was at full blast 10.000 RPM with 3km head wind.

Result. Neighbour is giving me evils.

[slofox]

A) Circumference of the string= Pi X 30cm = 94.25cm
The string revolves 10,000 times per minute = 94.25 x 10000= 942500cm per minute
1cm per minute= 0.0006 kmh x 942500 = 565.5kmh

Same answer I got...MUST be right then!

[mossy1200]

Weedeater should have guards on it to prevent peeble from being able to be shot out other than the front in which would be angled towards the uncut weeds that would slow or prevent the peeble from going anywhere. Unless you were to leave weedeater on its side running and the peebles were thrown into it. Im thinking refer the user manual for operating instructions.

[avgas]

Shit. By my calculations using my FX-82 scientific calculator, she'd be travelling at over mach 4. Oh, hang on, I am holding the calculator up side down.


Ok. Further following a prctical test in my driveway using a Ryobi 2 smoke weed eater and a 10mm round(ish) stone I can confirm that it hit the neighbours shed window from aprox 25 metres away. that was at full blast 10.000 RPM with 3km head wind.

Result. Neighbour is giving me evils.

So it didn't blow a hole in the garage?
Must be less that 50kph then?.....................................NOT 500KPH!

Sometimes I wonder if calculators make people stupid, or smarter?

[5150]

So it didn't blow a hole in the garage?
Must be less that 50kph then?.....................................NOT 500KPH!

Sometimes I wonder if calculators make people stupid, or smarter?

On closer inspection of the said shed window, I can confirm 3 things.

1) The stone did not leave any damage on the glass
2) The neighbour has a fine collection of nudie posters on his garage walls
3) His garage is a fucking mass