View Full Version : mathematicians i need help

3rd Apr 2006, 15:11
can someone tell me how you go about solving this question

a boy is tobogganing down a slope inclined at 25' (degrees) to the horizontal. the resistances to his motion amount to 15N. by modelling the boy and his toboggan as a single particle, find the mass of the boy and his toboggan when his acceleration is 3.9 metres per square second


Kalium Chloride
3rd Apr 2006, 15:42
OK - here goes:

Start with Newton's second law: Force = Mass x Acceleration

You already know the acceleration, and you know there's two forces to take into account:

(i) the component of gravity pulling the boy down the slope (mass x gravity x sin 25 degrees)

(ii) minus the resistance to motion acting in the opposite direction (15N)

So you know enough to solve your Newton equation: F = m x a

Overall force (mg x sin25) - 15 = 3.9m

Rearrange to give: m(g sin25 - 3.9) = 15

Taking gravity as 9.8m/s/s leaves you with: 0.24m = 15

...and therefore the mass 'm' = 62kg


green granite
3rd Apr 2006, 15:44
square second??? is that the same as a round cube/ :confused:

sorry I'll get my coat

Gingerbread Man
3rd Apr 2006, 15:48
Damn you! My chance to shine vanished!

Ah well. Seeing as I wrote it out for you, i might as well post it:


By the way, if you do an engineering degree you get the crap handwriting free of charge.

Ginger ;)

3rd Apr 2006, 15:48
Sorry, I think he went off at a tangent. :rolleyes:

3rd Apr 2006, 15:50
What is his mass if the slope is actually a conveyor belt?:E

3rd Apr 2006, 15:59
If the slope is a conveyor belt, take off 15.

This assumes you can take off.


3rd Apr 2006, 16:05
Whatif he's toboggoning inside an aircraft accelerating down the conveyor belt? :}

Gingerbread Man
3rd Apr 2006, 16:06
Oh no, you're not bringing that huge waste-of-time-discussion in here. This is for serious people with serious maths questions about... boys on toboggans :( .

Noah Zark.
3rd Apr 2006, 16:06
.......but only at 33.3 cycles per second (uphill) and only if the Lunar eclipse falls on a Leap Year Day.

Gingerbread Man
3rd Apr 2006, 16:08
Noah Zark, with that kind of language I think you want the Mornington Crescent thread. It's down the hall and to the left.

3rd Apr 2006, 16:10
No, this about toboggans. Sledges, or is that sleds, are down the hall. Or is that sleighs..... :confused: Well that's a troika of them anyway.... :}

ps. Is that monocycles, bicycles or tricycles...

3rd Apr 2006, 16:20
It's all downhill from here . . .

3rd Apr 2006, 16:23
Before outshining everyone with my complete lack of knowledge in physics, I'd nevertheless like to know: One assumes that the slope is snow-covered (hence toboggan)...this being the case, please supply the relevent data concerning snowfall, temperatures etc. over the preceding 12 months.

Uhmmm OK, so I just saw that you've provided the figure of 15N in lieu of all that. However, I still do not find it reasonable to assume a constant 15N resistance during the whole descent... :8

Gingerbread Man
3rd Apr 2006, 16:25
Didn't factor in air resistance either. Or the Corriolis effect. ;)

3rd Apr 2006, 16:27
the resistances to his motion amount to 15N.
Was he scared?

Noah Zark.
3rd Apr 2006, 16:31
Is the boy sitting upright, in which case he will eventually fall off, 'cos that's how girlies do it, or is he in the bellyflop position, in which case he will continue to accelerate until he caves his head in on the wall across the bottom of the hill?

3rd Apr 2006, 16:38
Where was the toboggan made?:}


Noah Zark.
3rd Apr 2006, 16:43
Is it the right kind of snow? We don't want any British Rail tomfoolery here.

3rd Apr 2006, 16:57
cheers guys :D :ok:

3rd Apr 2006, 17:13
I reckon that matamisa is really one of the boffins at the US MINOS (http://news.bbc.co.uk/2/hi/science/nature/4862112.stm) experiment only... by modelling the boy and his toboggan as a single particle they converted em into a neutrino, shot them towards a multi-million dollar detector 450 miles away through the centre of the earth and...uhmmm, lost em! ;)

Anyone seen a boy and his toboggan disguised as a neutrino recently?! :uhoh:

3rd Apr 2006, 17:23
Anyone seen a boy and his toboggan disguised as a neutrino recently?! :uhoh:
Isn't that racial indiscrimination?

huge forkbender
3rd Apr 2006, 17:39
Two atoms sat side by side.
One says to the other "Hey have you got one of my electrons, I'm missing one?"
"Are you sure?" says the other

"Yes I'm positive"

3rd Apr 2006, 17:45
How dare you G-CPTN?! According to the standard model, I believe that I merely resemble a strange and mostly charming if occasionally bottom-dwelling, large W bosom-respecting particle reputedly of little mass... :sad:

3rd Apr 2006, 19:39
With that much resistance to his motion, shouldn't he be taking Ex-Lax?

Gingerbread Man
3rd Apr 2006, 21:55
Now let's see someone really solve a problem ;)


Ginger :)

3rd Apr 2006, 23:11
Damnation to that infernal calculus.
Give me a good binomial theoram anyday.

6th Apr 2006, 02:26
Once upon a time I could write a subroutine to do a nested evaluation of a polynomial equation of any degree. Also its first derivative.

But now I just can't imagine why anyone would want to do such a silly thing. :ugh:

6th Apr 2006, 03:52
Of course, the discrepancy of 1kg is the difference between skipping off the earth's atmosphere and burning up on re-entry. . . :hmm: :rolleyes:
It's all Greek to me.

6th Apr 2006, 07:31
You should find it as easy as pi, then.

6th Apr 2006, 07:40
e by gum.....

6th Apr 2006, 07:42
*psi* :rolleyes:

I nu someone else would have a go.

Can't you do beta than that?

Not that I care one iota.

Hey, look, four in a rho!

Five, counting that! :}

6th Apr 2006, 12:06
I maintain that pi is an integer - it's just that we haven't got the base right yet.

7th Apr 2006, 09:13
".... the resistances to his motion amount to 15N ...."

I bet that made his eyes water!

Coincidence is a funny thing. Just yesterday I was listening to BBC Radio 4 (for some reason our cable radio & TV provider here in this part of CH has this included on his list - the only English language station on the list - which is FINE, except when they destroy the whole morning with bloody cricket commentary - I thought I'd left that behind when I left UK!!!) and I heard a programme with Penelope Keith remembering her Xmas TV show with Eric & Ernie ("Oh sorry, Derek" - "Not at all Mr. Moron" - etc, etc).

Does anyone else on here share my admittedly childish love of really awful puns and "silly" (but perfectly-timed) one liners? I'm thinking of stuff heard regularly in "Beyond our Ken" (Brown-Horrocks) and the one that still makes me fall about every time I think of it, even though I only saw it once, and that was years ago - a Morecombe & Wise TV show where they took the mickey out of the RFC. This had the, to me unforgetable, Eric reply to Ernie's "I'll go and service the Camel". It was of course "There's no answer to that".


Krgds to all