physics concept quesiton

[Eeezee]

Originally posted by: ledjani
Well I believe the answer is 0. The derivative of the velocity is acceleration. Thus whenever the graph of the velocity reaches its max, the derivative is 0. Thus the acceleration is 0. Because it is at rest acceleration wise, it has reached the top, and it isn't going up or down anymore.

If the acceleration were 0, then the particle would not have reached its max height in t > 0 seconds.

 

[Goosemaster]

Originally posted by: Heisenberg

Originally posted by: Goosemaster

Originally posted by: Heisenberg
/bangs head on desk at some replies



Newton must be spinning in his grave right now.

dude..by all means correct me...I sck at physics.


My first response would be to blurt out 9.8 but my reasoning, as you see it above, is what I would eventual utter to my furious and very angry physics prof.


by all means....enlghten us oh atomic master...

Plum pudding is delicious by the way...way better htan yoru stuff

I wasn't really meaning you specifically. I did post a reply earlier in the thread but apparently no one bothered to read it.

so in other words I shouch stick to engineering...anythign but civil sicne I don't want to casue another Marriot incident

 

[Wnh5001]

Originally posted by: Eeezee

Originally posted by: Wnh5001
a particle reaches it max height t= 2 seconds, what is the magnitude of its acceleration?

|hint|- the t=2 seconds doesnt mean anything =S, choose wisely,

a)19.6
b)9.81
c)0
d)-9.81

Wow, the world is so small. I graded a test with this exact question and these exact answers. Tell me, are you enrolled at the University of Arizona?

i made up answer a, cause i don't remember it the other 2 possible choices. the only ones i remembered were 9.8, 0 or -9.81, and there were two other choices,

for those who think the question is poorly worded, i would also agree, but thats life, these test makers need to make it tricky... or we would score 100's.

 

[JujuFish]

Originally posted by: Wnh5001
for those who think the question is poorly worded, i would also agree, but thats life, these test makers need to make it tricky... or we would score 100's.

Or they could just make it hard. There is no reason to have such a stupid question.

 

[KillerCharlie]

Originally posted by: ledjani
Well I believe the answer is 0. The derivative of the velocity is acceleration. Thus whenever the graph of the velocity reaches its max, the derivative is 0. Thus the acceleration is 0. Because it is at rest acceleration wise, it has reached the top, and it isn't going up or down anymore.

You suck at calculus.

 

[fornax]

Originally posted by: Heisenberg
/bangs head on desk at some replies

Newton must be spinning in his grave right now.

LOL!

 

[Yossarian]

B

 

[dighn]

Originally posted by: Heisenberg
/bangs head on desk at some replies



Newton must be spinning in his grave right now.

this thread should have been awfully short

 

[fornax]

Originally posted by: Wnh5001
for those who think the question is poorly worded, i would also agree, but thats life, these test makers need to make it tricky... or we would score 100's.

The question could have been worded better, but are you quoting the question verbatim?

Anyway, as Heisenberg said, as long as the particle is above the ground and no other forces are acting on it (e.g. air resistance, strong wind, etc), the acceleration is always 9.81 m/s^2 and because the question is about the magnitude, we don't have to worry about the sign either. It doesn't matter if the particle has reached max. height, or is falling, or is traveling upwards: the magnitude of the acceleration is always 9.81 m/s^2 as long as gravity is the only force that acts on it. So the correct answer is b)

 

[Titan]

Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

 

[Goosemaster]

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

So my dumbass status is revoked?


or not?

 

[Mo0o]

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

That is just.. so.. wrong

 

[Goosemaster]

Originally posted by: Mo0o

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

That is just.. so.. wrong

dammnit

 

[Titan]

Originally posted by: Goosemaster

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

So my dumbass status is revoked?


or not?

This is one of those situations where language confuses things. It is very easy for a teacher to expect a different answer because wording is so unclear. I science, you measure phenomena, not expect forces. I look at it as if there were another force, say wind resistance counteracting gravity and it was falling, the acceleration would be less than 9.8m/s. When you are standing on the ground, you are not accelerating, forces are canceling each other out.

But here's the annoying part, we cannot capture that exact instant of the apex of a projectile so it's a very hypothetical question.

EDIT: can people who think i'm wrong kindly explain the difference between a force and acceleration?

 

[Mo0o]

It's pretty simple. Fnet=M * A thus A= Fnet/M Mass is a constant quantity (in this instance atleast) and Fnet is just the gravitational pull between the object and the earth. So unless there wasn't gravity, there will be an acceleration. This is all in a very simplistic world with no wind resistance blabla

 

[Mo0o]

Originally posted by: Titan

Originally posted by: Goosemaster

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

So my dumbass status is revoked?


or not?

This is one of those situations where language confuses things. It is very easy for a teacher to expect a different answer because wording is so unclear. I science, you measure phenomena, not expect forces. I look at it as if there were another force, say wind resistance counteracting gravity and it was falling, the acceleration would be less than 9.8m/s. When you are standing on the ground, you are not accelerating, forces are canceling each other out.

But here's the annoying part, we cannot capture that exact instant of the apex of a projectile so it's a very hypothetical question.

This is clearly a high school physics question in an ideal world. Not to mention it's multiple choice so you're limited to the ideal answers. And no matter what world you're in 0 is still the wrong answer

 

[dighn]

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

the speed at any moment, by it self, has nothing to do with the acceleration. if there's no acceleration, why does the projectile go from 0 speed to increasingly downward velocity?

or looking it from the newton's law point of view: f = m*a, the net force here is the force of gravity or m*g, a is g as long as gravity is the only force acting on the body

 

[Mo0o]

Originally posted by: dighn

Originally posted by: Titan
Zero. AT one point in my life i did get 100s on physics exams.

Sounds like people are confusing forces and acceleration.

Under the influence of gravity, when a projectile reaches it's apex, it is not moving. Yes, the force of gravity is acring upon it, but at that instant, the upward momentum and the force of gravity cancel each other out. The result is it is not accelerating anywhere, in any direction.

The formula is position as a function of time.

First derivitave is velocity.

Second derivitave is acceleration.

No movement, no acceleration, period.

come on where do people get this stuff from?

the speed at any moment, by it self, has nothing to do with the acceleration. if there's no acceleration, why does the projectile go from 0 speed to increasingly downward velocity?

or looking it from the newton's law point of view: f = m*a, the net force here is the force of gravity or m*g, a is g as long as gravity is the only force acting on the body

please stop beating this dead horse

Really makes you wonder how he made 100s on his physics tests

 

[Titan]

Acceleration is the derivitave of velocity. According to Issac Newton. Granddaddy of calculus. Look it up. Since the question does not ask for direction, magnitude is simple.

Acceleration is a charictaristic mesurement of motion, not the forces causing the motion, the distinction is subtle.

 

[Mo0o]

Originally posted by: Titan
Acceleration is the derivitave of velocity. According to Issac Newton. Granddaddy of calculus. Look it up. Since the question does not ask for direction, magnitude is simple.

You can have zero velocity while still having an acceleration. Acceleration is the changing of velocity. which means you have to take two data points to acutally find acceleration. So just finding the velocity at one point doesn't mean sh1t. You need two data points. You really need to learn how math works before talking

 

[Titan]

Originally posted by: Mo0o

Originally posted by: Titan
Acceleration is the derivitave of velocity. According to Issac Newton. Granddaddy of calculus. Look it up. Since the question does not ask for direction, magnitude is simple.

You can have zero velocity while still having an acceleration. Acceleration is the changing of velocity. which means you have to take two data points to acutally find acceleration. So just finding the velocity at one point doesn't mean sh1t. You need two data points. You really need to learn how math works before talking

So if you're not moving in any direction, you are accelerating? If so, where? How fast? I say 0.0m/s^2 while still in a reference frame.

 

[dighn]

Originally posted by: Mo0o
Really makes you wonder how he made 100s on his physics tests

I hope he just forgot the stuff or the kids at his school got/are getting some crappy education.

 

[Mo0o]

Allow me to break it down further.

X=VoT + .5 AT^2
dX/dT = V = Vo + AT
dV/dT = A

Can you follow that? As you can see, there are instances of T where V is zero while still maintaining an A tahts nonzero

 

[dighn]

Originally posted by: Titan

Originally posted by: Mo0o

Originally posted by: Titan
Acceleration is the derivitave of velocity. According to Issac Newton. Granddaddy of calculus. Look it up. Since the question does not ask for direction, magnitude is simple.

You can have zero velocity while still having an acceleration. Acceleration is the changing of velocity. which means you have to take two data points to acutally find acceleration. So just finding the velocity at one point doesn't mean sh1t. You need two data points. You really need to learn how math works before talking

So if you're not moving in any direction, you are accelerating? If so, where? How fast? I say 0.0m/s^2 while still in a reference frame.

yes! downward.

acceleration is dv/dt, if it's zero, then the speed does not change from 0. you keep bringing up newton, why do you ignore his laws of motion? ok so his original equation is something like (so I hear) d(moement)/dt = F, however momentum is mv, so that's still m(dv/dt) = F = m*a = f

 

[Mo0o]

Originally posted by: Titan

Originally posted by: Mo0o

Originally posted by: Titan
Acceleration is the derivitave of velocity. According to Issac Newton. Granddaddy of calculus. Look it up. Since the question does not ask for direction, magnitude is simple.

You can have zero velocity while still having an acceleration. Acceleration is the changing of velocity. which means you have to take two data points to acutally find acceleration. So just finding the velocity at one point doesn't mean sh1t. You need two data points. You really need to learn how math works before talking

So if you're not moving in any direction, you are accelerating? If so, where? How fast? I say 0.0m/s^2 while still in a reference frame.

Having a zero velocity at one moment in time doesn't mean the object wont be moving in the next moment. negating air resistance and wind, acceleration is constant for an object in the air. Just because its velocity is zero at any ONE specific time doesn't mean its not accelerating