Hovercraft B/C

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Re: Hovercraft B/C

Postby Adi1008 » Sun Apr 29, 2018 2:34 pm

randomperson123 wrote:Is the hovercraft written test self-scheduled at nationals?

Based on the tentative schedule in the rulebook, hovercraft is completely self schedule.
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Re: Hovercraft B/C

Postby Birdmusic » Wed May 02, 2018 3:06 am

BasuSiddha23 wrote:How many rolls of pennies can your hovercrafts hold?

I just want to see our performance compared to other teams.


4 at most with full batteries. (yeah i can't build)
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Re: Hovercraft B/C

Postby jgrischow1 » Wed May 02, 2018 11:43 am

Sorry if something like this has already been posted, but we found a really good way to increase the number of pennies we could hold. When my kids were just randomly poking holes in the bottom of their skirt, they could only get 3-4 pennies on. We created a simple device in which graph paper was taped on to a piece of cardboard. We then poked thumbtacks through the intersections of the graph paper. We must have had hundreds of tacks on it. The kids pierced their skirts with the device, and the even holes really helped, enabling them to get 12-13 penny roles and a 15 second time.

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Re: Hovercraft B/C

Postby LittyWap » Thu May 03, 2018 3:54 am

jgrischow1 wrote:Sorry if something like this has already been posted, but we found a really good way to increase the number of pennies we could hold. When my kids were just randomly poking holes in the bottom of their skirt, they could only get 3-4 pennies on. We created a simple device in which graph paper was taped on to a piece of cardboard. We then poked thumbtacks through the intersections of the graph paper. We must have had hundreds of tacks on it. The kids pierced their skirts with the device, and the even holes really helped, enabling them to get 12-13 penny roles and a 15 second time.




Seeing as how im not making it to Nats this year and this event is leaving in 2019, I should tell you that this was major to the success of my craft. It's like an air hockey table, where the holes restrict the volumetric flow and increase the static pressure.
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Re: Hovercraft B/C

Postby IvanGe » Sat May 05, 2018 8:09 pm

Does anyone know if they will give you credit for an answer being 51.50N when the answer key says 51.52N? Does that small difference affect if you get credit or not?
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Re: Hovercraft B/C

Postby MIScioly1 » Sat May 05, 2018 8:32 pm

IvanGe wrote:Does anyone know if they will give you credit for an answer being 51.50N when the answer key says 51.52N? Does that small difference affect if you get credit or not?


100% dependent on the supervisor. If the supervisor is requesting the calculation to be done in a certain way using sig figs, then I suppose that difference could affect credit. That being said, I would give it full credit if I were the supervisor.
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Re: Hovercraft B/C

Postby MIScioly1 » Sat May 05, 2018 8:33 pm

MIScioly1 wrote:
IvanGe wrote:Does anyone know if they will give you credit for an answer being 51.50N when the answer key says 51.52N? Does that small difference affect if you get credit or not?


100% dependent on the supervisor. If the supervisor is requesting the calculation to be done in a certain way using sig figs, then I suppose that difference could affect credit. That being said, I would give it full credit if I were the supervisor.


I assume most would have no problem with it, though. (sorry for double post)
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Re: Hovercraft B/C

Postby CMS AC » Sat May 05, 2018 9:38 pm

How significant is sig figs though? Like how many points would they take off?(No pun intended)

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Re: Hovercraft B/C

Postby antoine_ego » Sat May 05, 2018 9:58 pm

CMS AC wrote:How significant is sig figs though? Like how many points would they take off?(No pun intended)

Depends on the test and test writer. For example, on Optics MIT, you lost half credit if your sig figs were off. I'd read the directions carefully; sometimes they ask for a fixed number (i.e. Astronomy MIT).
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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » Sun May 06, 2018 1:40 am

MIScioly1 wrote:
IvanGe wrote:Does anyone know if they will give you credit for an answer being 51.50N when the answer key says 51.52N? Does that small difference affect if you get credit or not?


100% dependent on the supervisor. If the supervisor is requesting the calculation to be done in a certain way using sig figs, then I suppose that difference could affect credit. That being said, I would give it full credit if I were the supervisor.

Also dependent on the question. If it's a straightforward one-step or two-step calculation, it's harder to deem it creditworthy than, say, if it was five or six calculations.

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Re: Hovercraft B/C

Postby IvanGe » Sat May 12, 2018 8:39 pm

i didn't feel like posting this in the Question Marathon, so i guess i'll just post it here because it's more like a check-my-work-please.

A bungee jumper of mass 40 kg is attached to a bungee cord with a constant of 80 n/m. The unstretched length of the bungee is 15m. What is the maximum velocity of the jumper? (g = 10 m/s^2)

I did it by using the potential energy of the spring and when it is at maximum velocity, the potential energy should completely change into kinetic energy(even though it doesn't in this case). So :

Hooke's law
f = kx to find x

PE = KE + PEspring
mgh = 1/2kx^2 + 1/2mv^2

assuming h is equal to 15 + x

The answer key said 17.32 m/s and I did not get that by doing this, instead I got 18.71 m/s
Last edited by IvanGe on Sun May 13, 2018 2:37 am, edited 2 times in total.
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Re: Hovercraft B/C

Postby MattChina » Sun May 13, 2018 2:12 am

IvanGe wrote:i didn't feel like posting this in the Question Marathon, so i guess i'll just post it here because it's more like a check-my-work-please.

A bungee jumper of mass 40 kg is attached to a bungee cord with a constant of 80 n/m. The unstretched length of the bungee is 15m. What is the maximum velocity of the jumper? (g = 10 m/s^2)

I did it by using the potential energy of the spring and when it is at maximum velocity, the potential energy should completely change into kinetic energy(even though it doesn't in this case). So :

Hooke's law
f = kx to find x

PE = KE + PEspring
mgh = 1/2kx^2 + 1/2mv^2

assuming h is equal to 15 + x

The answer key said 17.32 m/s and I did not get that by doing this, instead I got 18.71 m/s^.


Idk man, Got the same answer.
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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » Sun May 13, 2018 3:00 am

MattChina wrote:
IvanGe wrote:i didn't feel like posting this in the Question Marathon, so i guess i'll just post it here because it's more like a check-my-work-please.

A bungee jumper of mass 40 kg is attached to a bungee cord with a constant of 80 n/m. The unstretched length of the bungee is 15m. What is the maximum velocity of the jumper? (g = 10 m/s^2)

I did it by using the potential energy of the spring and when it is at maximum velocity, the potential energy should completely change into kinetic energy(even though it doesn't in this case). So :

Hooke's law
f = kx to find x

PE = KE + PEspring
mgh = 1/2kx^2 + 1/2mv^2

assuming h is equal to 15 + x

The answer key said 17.32 m/s and I did not get that by doing this, instead I got 18.71 m/s^.


Idk man, Got the same answer.

I got the same answer.
For those confused about how the answer was obtained (like I was)
At any particular moment at time, the Law of Conservation of Energy applies.

The left side is the gravitational potential energy of the bungee jumper before he jumps (h is the distance from this height to the height of the bungee jumper at this particular point in time).
The right side is the elastic potential energy of the cord (follows Hooke's law, where x is the additional stretchage of the cord past 15 m) and the kinetic energy of the bungee jumper.
To proceed, we need one more equation:

This is because at any given point, h is the length of the bungee cord.
Plug in values:

Simplify:

Solve for :

At this point, you can find the maximum by (1) finding the maximum of the parabola and then square rooting it or (2) plugging in your graphing calculator and letting it find the maximum for you.

Either way, you get the answer

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Re: Hovercraft B/C

Postby IvanGe » Sun May 13, 2018 3:20 am

UTF-8 U+6211 U+662F wrote:
MattChina wrote:
IvanGe wrote:i didn't feel like posting this in the Question Marathon, so i guess i'll just post it here because it's more like a check-my-work-please.

A bungee jumper of mass 40 kg is attached to a bungee cord with a constant of 80 n/m. The unstretched length of the bungee is 15m. What is the maximum velocity of the jumper? (g = 10 m/s^2)

I did it by using the potential energy of the spring and when it is at maximum velocity, the potential energy should completely change into kinetic energy(even though it doesn't in this case). So :

Hooke's law
f = kx to find x

PE = KE + PEspring
mgh = 1/2kx^2 + 1/2mv^2

assuming h is equal to 15 + x

The answer key said 17.32 m/s and I did not get that by doing this, instead I got 18.71 m/s^.


Idk man, Got the same answer.

I got the same answer.
For those confused about how the answer was obtained (like I was)
At any particular moment at time, the Law of Conservation of Energy applies.

The left side is the gravitational potential energy of the bungee jumper before he jumps (h is the distance from this height to the height of the bungee jumper at this particular point in time).
The right side is the elastic potential energy of the cord (follows Hooke's law, where x is the additional stretchage of the cord past 15 m) and the kinetic energy of the bungee jumper.
To proceed, we need one more equation:

This is because at any given point, h is the length of the bungee cord.
Plug in values:

Simplify:

Solve for :

At this point, you can find the maximum by (1) finding the maximum of the parabola and then square rooting it or (2) plugging in your graphing calculator and letting it find the maximum for you.

Either way, you get the answer


aight guys I guess the answer key was wrong? It's from Cypress Falls Invitational Division C for those wondering.
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Re: Hovercraft B/C

Postby LittyWap » Thu May 17, 2018 10:13 pm

Thought you guys would want to see this. Anyone else ready for Nats??

https://imgur.com/a/5Pw0St2
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