NationStates Jolt Archive

ive been working on my physics hw since lasnt night. i dont get hardly any of this

pplease help me on just one other impossible question

Your school science club has devised a special event for homecoming. You've attached a rocket to the rear of a small car that has been decorated in the blue-and-gold school colors. The rocket provides a constant acceleration for 9.0s. As the rocket shuts off, a parachute opens and slows the car at a rate of 5.0m/s^2. The car passes the judges' box in the center of the grandstand, 990m from the starting line, exactly 12s after you fire the rocket.
What is the car's speed as it passes the judges?



i guessed 15, but i was wrong, and now i have only two tries remaining :headbang:

Hi,

There's a guy at the region "The End of the Universe" named Zypher Hunter who knows a lot about Physics. I'm sure he can definitely help you out. Send him a telegram or something. Good luck.

i guessed 15, but i was wrong, and now i have only two tries remaining :headbang:

Did you really "guess" - or did you do some work and got the wrong answer ?
In the second case - show your work, and people will be able to point at the flaw ;)

Did you really "guess" - or did you do some work and got the wrong answer ?
In the second case - show your work, and people will be able to point at the flaw ;)

well it was merely a simple formula:

a=v/t
5=v/3
v=15m/s

the only problem with this answer is that the rocket didnt come to a stop, but kept on going after it passed the judges

Pics! I want pics!

Hi,

There's a guy at the region "The End of the Universe" named Zypher Hunter who knows a lot about Physics. I'm sure he can definitely help you out. Send him a telegram or something. Good luck.

thanks, ill look into that, but im definately getting a tutor. this is just so dam hard

I got 271.875 meters per second. Might be wrong, but here is how I did it:

Assuming that y is the amount it accelerated per second in the first half, then the speeds go like this per second

1 2 3 4 5 6 7 8 9 10 11 12
y 2y 3y 4y 5y 6y 7y 8y 9y 9y-5 9y-10 9y-15

The total of distance traveled is 32y-30 therefore.

32y-30 = 990
32y = 1020
y = 31.875

(31.875 x 9) - 15 = 271.875m/s

ive been working on my physics hw since lasnt night. i dont get hardly any of this

pplease help me on just one other impossible question

Your school science club has devised a special event for homecoming. You've attached a rocket to the rear of a small car that has been decorated in the blue-and-gold school colors. The rocket provides a constant acceleration for 9.0s. As the rocket shuts off, a parachute opens and slows the car at a rate of 5.0m/s^2. The car passes the judges' box in the center of the grandstand, 990m from the starting line, exactly 12s after you fire the rocket.
What is the car's speed as it passes the judges?



i guessed 15, but i was wrong, and now i have only two tries remaining :headbang:

You're also hopeless with words, why is it "hopeless versus physics"?

Jesus F Christ, can someone please get America a dictionary? constant use of vs in places where it makes absolutely NO SENSE WHAT SO EVER!

ive been working on my physics hw since lasnt night. i dont get hardly any of this

pplease help me on just one other impossible question

Your school science club has devised a special event for homecoming. You've attached a rocket to the rear of a small car that has been decorated in the blue-and-gold school colors. The rocket provides a constant acceleration for 9.0s. As the rocket shuts off, a parachute opens and slows the car at a rate of 5.0m/s^2. The car passes the judges' box in the center of the grandstand, 990m from the starting line, exactly 12s after you fire the rocket.
What is the car's speed as it passes the judges?



i guessed 15, but i was wrong, and now i have only two tries remaining :headbang:

the car accereletes with 'a' for 9 secs, its speed at the time the parachute opens is v1=a*9
next we use a sligthly more complicated equation:
s=v*t+(a/2)*t^2
s, the distance is 990m
this adds up from two parts the accelerating part, and the decelerating.

so we get 990=0*9+(a/2)*9^2(this wat he acc. part)+v1*3+(-5/2)*3^2(dec part)

substitute v1=a*9, solve the equation, and we get: a=16.5, this is the acceleration of the rocket. so the speed after 9 secs is v1=16.5
*9=148.5
from this point, the car deccelartes v2=v1-5*3=133.5

You're also hopeless with words, why is it "hopeless versus physics"?
Jesus F Christ, can someone please get America a dictionary? constant use of vs in places where it makes absolutely NO SENSE WHAT SO EVER!
Calm down. Its Latin. Not American. :p

edit 120m/s when it passes the judge box

i had a + for a - in one term at my first attempt

ive been working on my physics hw since lasnt night. i dont get hardly any of this

pplease help me on just one other impossible question

Your school science club has devised a special event for homecoming. You've attached a rocket to the rear of a small car that has been decorated in the blue-and-gold school colors. The rocket provides a constant acceleration for 9.0s. As the rocket shuts off, a parachute opens and slows the car at a rate of 5.0m/s^2. The car passes the judges' box in the center of the grandstand, 990m from the starting line, exactly 12s after you fire the rocket.
What is the car's speed as it passes the judges?



i guessed 15, but i was wrong, and now i have only two tries remaining :headbang:

The rocket's acceleration isn't known?

This is a little equations of motions question with several unknowns. The trick is to express all of the unknowns in terms of one single variable, break the motion down into two separate stages and use the equations of motion to derive expressions for the various properties. For instance, to get you started, we can represent the velocity after 9 seconds in the equation

velocity after 9 seconds = Initial velocity + acceleration*time
v = 0 + 9*a
= 9a

which we can then use in other equations. Try things like that with a few other things like the distance after the first 9 seconds and so on.

Three things worth remembering;

1) The initial speed is zero.
2) The final speed after the first 9 seconds is equivilent to the initial speed of the last 3 seconds.
3) When in the last 3 seconds, we use a negative acceleration to represent a slowing down.

Calm down. Its Latin. Not American. :p

:P

Well, I see it all the time; I'm thinking to myself, "how is there a competition between these two things' which is what versus implies.

114m/s when it passes the judge box

I got 120m/s with the original a = 15 m/s^2 . .. intruiging ;)
*goes off to recheck his math*

I got 120m/s with the original a = 15 m/s^2 . .. intruiging ;)
*goes off to recheck his math*jaja you are right, 15m/s^2 acceleration and 120m/s velocity, on my first try i missed the - on the 1/2*5m/s^2*(3s)^2

Haven't got a bloody clue! I hate both maths and physics and chemistry. That's why I turned to writing. Good job I can speel and rite proper!

Others beat me to it.

jaja you are right, 15m/s^2 acceleration and 120m/s velocity, on my first try i missed the - on the 1/2*5m/s^2*(3s)^2

Cool- inserting a =15 in the equations and solving for x also results in 990; so I'm pretty sure we are right :)

Basic outline of the steps:
General equations x(t) = 0,5 a t^2 + v(0) t + x(0) v(t) = a t + v(0)
So for the rocket at t=9: x(9) = 40,5 a v(9) = 9a
Setting t2= t - 9, and inserting the shute decelleration:
x(t2) = 0,5 (-5) t2^2 + 9 a t2 + 40,5 a = -2,5 t2^2 + 9 a t2 + 40,5 a
v(t2) = -5 t2 + 9a
At t2 = 12-9 = 3 we get: x(t2=3) = -22,5 + 27 a + 40,5 a = 67,5 a - 22,5 = 990m v(t2=3)= -15 + 9a
Solving the x-equation for a yields a = 15
Inserting a=15 in the equation for v yields v(t2=3) = 120

Voila :)

:P

Well, I see it all the time; I'm thinking to myself, "how is there a competition between these two things' which is what versus implies.


Well actually, saying I'm hopeless vs physics hw would imply thats its The author vs physics

Just like if you said boxerA is hopeless verses boxerB. That statement wouldn't imply that the match is BoxerB fighting against the word hopeless.

And it definatley sounds to me like the author is in a brawl with physics homework.

Well actually, saying I'm hopeless vs physics hw would imply thats its The author vs physics

Just like if you said boxerA is hopeless verses boxerB. That statement wouldn't imply that the match is BoxerB fighting against the word hopeless.

And it definatley sounds to me like the author is in a brawl with physics homework.

Then wouldn't it be 'hopeless guy vs. physics homework"'

Hi,

There's a guy at the region "The End of the Universe" named Zypher Hunter who knows a lot about Physics. I'm sure he can definitely help you out. Send him a telegram or something. Good luck.


:confused: :mad: :sniper:

Go down to the recruiter's office now. You're hopeless.