physics concept quesiton

[thereaderrabbit]

A or B, cause it just depends on the units.

 

[Schfifty Five]

Originally posted by: ledjani
I am sticking with my answer at 0 because when it reaches a maximum velocity it isn't accelerating or decelaring yet. Thus it is 0. The question asks for the acceleration, not for the force. I think people are confusing it with the forces on the object rather than the acceleration the ball is going.

I seriously hope you are not trolling and that you genuinely believe the answer is 0.

If it is the latter, then I will try to explain.

Imagine you threw a ball from your hand upward. You initially put some force into throwing the ball which results in it going upward. At the same time, the gravitational force has been affecting the ball even from the start (@ 9.8 m/s^2). However, your upward thrown initially was much greater than 9.8m/s^2 so it went upward.

Now, once the ball leaves your hand, that upward force/acceleration that you gave it is now gone and only gravity is acting upon it.

Even though the ball is traveling upward, gravity is still working it's magic by slowing it down and eventually, the ball comes to a maximum height (aka NO MORE UPWARD TRAVELING). At the MAXIMUM HEIGHT, the velocity is 0, BUT gravity is still working its magic.

The ball is now travelling back to earth b/c of gravity which has been acting upon the ball the entire time even when the ball was going upward.

 

[DaShen]

Originally posted by: Cooler

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

-9.81 the pull of graity in the negitive direction.

QFT... duh

 

[Brainonska511]

This thread is ridiculous.

The answer must be positive because it is asking for MAGNITUDE, which is always positive.
The answer cannot be 0 because gravity is always acting upon the object and the fact that it reaches a maximum height means that there is some kind of downward force acting upon the object.
This is obviously a simple physics problem and there should be no question that it can be assumed that the object is close to the surface of the Earth and that there are no forces, other than gravity, acting upon the object.

 

[slayer202]

the SPEED of the particle would be 0, because at the peak it is basically stopped, however gravity never stops so it is always accelerating at -9.8 m/s

 

[saahmed]

its obviously 9.8 m/s/s. The only acceleration acting on it is that of gravity, though its velocity is changing. And it is not negative, because acceleration has no direction.

 

[Brainonska511]

Originally posted by: saahmed
its obviously 9.8 m/s/s. The only acceleration acting on it is that of gravity, though its velocity is changing. And it is not negative, because acceleration has no direction.

Acceleration does have a direction. The only reason the answer in this thread is 9.8m/s^2 is because it is asking for the MAGNITUDE of the acceleration.

 

[aigomorla]

Originally posted by: Brainonska511
This thread is ridiculous.

The answer must be positive because it is asking for MAGNITUDE, which is always positive.
The answer cannot be 0 because gravity is always acting upon the object and the fact that it reaches a maximum height means that there is some kind of downward force acting upon the object.
This is obviously a simple physics problem and there should be no question that it can be assumed that the object is close to the surface of the Earth and that there are no forces, other than gravity, acting upon the object.

:thumbsup:

Asking for magnitude which is always possitive. Acceleration is negitive since the object slows down at top. This is a really gay question, but the responses to it is really funny. This is almost as bad as the airplane on tread mill question.

 

[inveterate]

OMG u freaking n00b,,

 

[DrPizza]

Originally posted by: 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.

lmao at this thread!!

Not only that, but if the particle reached its maximum height (and was thrown vertically) AND, the acceleration at that moment was 0, then the object would remain there. After all, with 0 acceleration, the velocity wouldn't change. Therefore, the velocity would remain zero and the object would just sort of hover... That'd be an interesting world indeed!

9.81m/s/s FTW!

And, for the "acceleration of gravity is -9.81m/s/s" (including the direction) the direction can be chosen arbitrarily. Upward can be considered either positive or negative (as it sometimes is). i.e. in problems where you drop a rock off a bridge, it's much more convenient to define the bridge as displacement = 0 and downward as the positive direction.

 

[DrPizza]

Originally posted by: aigomorla

Originally posted by: Brainonska511
This thread is ridiculous.

The answer must be positive because it is asking for MAGNITUDE, which is always positive.
The answer cannot be 0 because gravity is always acting upon the object and the fact that it reaches a maximum height means that there is some kind of downward force acting upon the object.
This is obviously a simple physics problem and there should be no question that it can be assumed that the object is close to the surface of the Earth and that there are no forces, other than gravity, acting upon the object.

:thumbsup:

Asking for magnitude which is always possitive. Acceleration is negitive since the object slows down at top. This is a really gay question, but the responses to it is really funny. This is almost as bad as the airplane on tread mill question.

As I stated a post or so ago in this thread, a coordinate system is arbitrary. You're saying that acceleration is negative because the object slows down at the top? Then, as the ball falls back to earth, and it speeds up, are you suddenly going to decide to change your acceleration to positive? The *speed* decreases until the object reaches its highest point. Then, the *speed* increases. However, you can say either the velocity decreases continuously from the initial velocity to 0 to a negative velocity on the way down --- or the velocity increases continuously from a negative value to 0 at its peak to a positive value on the way back down. It all depends on whether you define up as positive or up as negative. It's entirely arbitrary, but generally in this particular type of problem, up is defined as positive and down as negative. That, however, is not a rule.

Nonetheless, my point is that "speed" (slowing down or speeding up) has nothing to do with the sign of acceleration. If acceleration is positive, the object can be either slowing down or speeding up. And, if acceleration is negative, the object can be either slowing down or speeding up.

 

[Crescent13]

I'm just in 9th grade, but don't we need to know the weight of the object? If an object reaches it's max height in two seconds, don't we need to know how heavy it was so that we can figure out how much force was appliet to make it do that? Excuse me if I sound like a n00b I havn't started studying this stuff yet.

 

[Mo0o]

Originally posted by: Crescent13
I'm just in 9th grade, but don't we need to know the weight of the object? If an object reaches it's max height in two seconds, don't we need to know how heavy it was so that we can figure out how much force was appliet to make it do that? Excuse me if I sound like a n00b I havn't started studying this stuff yet.

negative. F=ma, increasing the mass will increase the force but A will still stay the same. Changing m wont change a

 

[Brainonska511]

wtf... why is this thread still here. We have thoroughly gone over the acceleration and have determined that many people simply don't know physics. I wish this thread would just be allowed to drop back off the front page of OT.

 

[JujuFish]

Originally posted by: Brainonska511
wtf... why is this thread still here. We have thoroughly gone over the acceleration and have determined that many people simply don't know physics. I wish this thread would just be allowed to drop back off the front page of OT.

You're not helping any by bumping it back to the top.

 

[Yossarian]

Originally posted by: Crescent13
I'm just in 9th grade, but don't we need to know the weight of the object? If an object reaches it's max height in two seconds, don't we need to know how heavy it was so that we can figure out how much force was appliet to make it do that? Excuse me if I sound like a n00b I havn't started studying this stuff yet.

it doesn't matter how much force was applied, because the instant the particle starts moving the only force acting on it is gravity.

 

[EliteXen]

Originally posted by: Yossarian

Originally posted by: Crescent13
I'm just in 9th grade, but don't we need to know the weight of the object? If an object reaches it's max height in two seconds, don't we need to know how heavy it was so that we can figure out how much force was appliet to make it do that? Excuse me if I sound like a n00b I havn't started studying this stuff yet.

it doesn't matter how much force was applied, because the instant the particle starts moving the only force acting on it is gravity.

Don't forgot the frictional force from air resistance

-Sorry, just had to throw my two cents in.

 

[Beige]

this just shows that Physics kicks Chemistry's butt any day.
Physics <3 FTW

 

[Crescent13]

Originally posted by: Yossarian

Originally posted by: Crescent13
I'm just in 9th grade, but don't we need to know the weight of the object? If an object reaches it's max height in two seconds, don't we need to know how heavy it was so that we can figure out how much force was appliet to make it do that? Excuse me if I sound like a n00b I havn't started studying this stuff yet.

it doesn't matter how much force was applied, because the instant the particle starts moving the only force acting on it is gravity.

ah. That makes sense. Thanks!

 

[xrax]

at t =2 s the acceleration is 0, at t > 2s the acceleration is 9.81 m/s/s.

 

[Brainonska511]

Originally posted by: xrax
at t =2 s the acceleration is 0, at t > 2s the acceleration is 9.81 m/s/s.

You are either an idiot or you just don't know physics. I hope for the latter. Acceleration is ALWAYS 9.81m/s/s after the ball is thrown. IT DOESN'T HAVE ANY FORCES ACTING ON IT BESIDES GRAVITY, THEREFORE ACCELERATION DOES NOT CHANGE.

Anyone else want to post something about how the acceleration is 0?

 

[Yossarian]

Originally posted by: Brainonska511

Originally posted by: xrax
at t =2 s the acceleration is 0, at t > 2s the acceleration is 9.81 m/s/s.

You are either an idiot or you just don't know physics. I hope for the latter. Acceleration is ALWAYS 9.81m/s/s after the ball is thrown. IT DOESN'T HAVE ANY FORCES ACTING ON IT BESIDES GRAVITY, THEREFORE ACCELERATION DOES NOT CHANGE.

Anyone else want to post something about how the acceleration is 0?

I would like to as a joke, but I'm afraid you might kill me and my family.

 

[Wnh5001]

Originally posted by: Yossarian

Originally posted by: Brainonska511

Originally posted by: xrax
at t =2 s the acceleration is 0, at t > 2s the acceleration is 9.81 m/s/s.

You are either an idiot or you just don't know physics. I hope for the latter. Acceleration is ALWAYS 9.81m/s/s after the ball is thrown. IT DOESN'T HAVE ANY FORCES ACTING ON IT BESIDES GRAVITY, THEREFORE ACCELERATION DOES NOT CHANGE.

Anyone else want to post something about how the acceleration is 0?

I would like to as a joke, but I'm afraid you might kill me and my family.

hehe, >_<, well i haven;t gotten my test yet, but i am pretty sure its 9.8 m/s2. im on friction and static friction and it looks pretty simple yet i dont get it.. its not the math.. its teh evil conceps...

 

[coomar]

Originally posted by: EliteXen

Originally posted by: Yossarian

Originally posted by: Crescent13
I'm just in 9th grade, but don't we need to know the weight of the object? If an object reaches it's max height in two seconds, don't we need to know how heavy it was so that we can figure out how much force was appliet to make it do that? Excuse me if I sound like a n00b I havn't started studying this stuff yet.

it doesn't matter how much force was applied, because the instant the particle starts moving the only force acting on it is gravity.

Don't forgot the frictional force from air resistance

-Sorry, just had to throw my two cents in.

I explained earlier why wind resistance wouldn't effect the air resistance at the apex

and g is not constant around the world, it varies froum 9.79 to 9.84 (i'm not sure if it goes that high)

crescent13, the weight of the object is the mass times the gravitational constant

it is the gravitational force that is responsible for the acceleration downwards, there is no other force acting on it at the apex (since velocity is zero at the apex, wind resistance which is dependent on velocity is zero)

 

[Brainonska511]

Originally posted by: Yossarian

Originally posted by: Brainonska511

Originally posted by: xrax
at t =2 s the acceleration is 0, at t > 2s the acceleration is 9.81 m/s/s.

You are either an idiot or you just don't know physics. I hope for the latter. Acceleration is ALWAYS 9.81m/s/s after the ball is thrown. IT DOESN'T HAVE ANY FORCES ACTING ON IT BESIDES GRAVITY, THEREFORE ACCELERATION DOES NOT CHANGE.

Anyone else want to post something about how the acceleration is 0?

I would like to as a joke, but I'm afraid you might kill me and my family.

lol