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Anyone please help me with LIMITING REACTANT IN CHEMISTRY any notes or guide me .........?
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Biology; Chemistry; Physics: Post your doubts here!
- Thread starter scouserlfc
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Whenever an object falls, the acceleration depends on the presence of air.
If the object is falling in a region without air resistance, then the acceleration of free-fall will be 10 m/s^2 till the moment the object hits the ground. It won't decrease to 0, and Terminal velocity won't be reached, since the object will continue to increase in speed at the rate of 10 m/s^2.
But, if an object falls in air resistance.. then the initial acceleration is 10 m/s^2.. but as its speed increases, the air resistance increases due to which the resultant force decreases and the acceleration decreases to 9, then to 8 and finally becomes zero when the weight and the air resistance become balanced. At this point terminal velocity is reached. Acceleration is zero.
If you look at the following MCQ from June 2006 paper 1..
The answer to this is C.
Now a small stone is falling from the top of the ladder.
They haven't mentioned if air resistance is present or not, but we can assume that it is.
Now the answer is C.. as it is the only logical explanation, but in C we can see that the gradient of the speed-time graph is constant..
Doesn't that mean there is a constant acceleration?
One thing we know for sure, is the distance of falling is very less, as it is falling from the top of a ladder.
It won't have time to reach terminal velocity, but isn't the acceleration supposed to decrease, even if only a little?
The stone will fall in a few seconds.. but still there is supposed to be an increase in speed, an increase in air resistance and a decrease in the acceleration.
But this graph shows clearly that there was no decrease in acceleration.
From this i formulated that whenever a question comes about a heavy object falling from a small distance above the ground, i should always assume that the acceleration will be constant 10 m/s^2 till the object hits the ground as it won't have enough time to increase in speed and thus increase the air resistance to decrease the acceleration.
Now, i recently encountered the following question in my exam, from May-June 2012 paper 1:
Now, in this question as you see, instead of the object falling in air, it is falling in thick oil.
We can assume that the same phenomenon takes place here, as it does when objects free fall in air..
The object will start to accelerate at 10 m/s^2 and gradually the acceleration will decrease.
But since i had finalized in the previous MCQ, the one posted before this one, that heavy objects (Stones, steel balls) accelerate at a constant rate in the first few seconds. Even if their acceleration decreases, it should be considered constant as the previous MCQ shows a straight line in the speed-time graph proving that there was a constant acceleration.
Now, this new question states ''During the first few CENTIMETERS''... it clearly mentions CENTIMETERS.
If the initial acceleration is 10 m/s^2 .. it can be visualized that within a second the steel ball would have traveled 10 m or 1000 cm.
And there would have been an increase in speed by 10 m/s..
But since it asks about the ''First few centimeters'' we can assume that they are talking about the first 10-20 cm maximum. That is a ''few''.. maybe even 5 cm.
Since, the acceleration was 10 m/s^2 in the start, it would have reduced by only a minute value in the first few centimetes.
I concluded in the previous question that heavy objects falling in the first few seconds, can be considered constant acceleration as the graph shows a straight line in the previous question. Implying the same concept here, keeping in mind they were talking about the ''First few centimeters''.. i thought that this can also be assumed to have constant acceleration in the first few seconds.. The first two options talk about Constant acceleration, but B says about constant accleration less than 10 m/s^2. Obviously it would be a little less than 10, so i selected B, based on the concept i had built in the previous MCQ which shows a straight line for the free-fall of a stone, before it hits the ground (Which would have taken seconds).
But the answer turns out to be C. ._.
Obviously, there would be a decrease in acceleration, OF COURSE.. but the previous MCQ shows a straight line.. and this new MCQ clearly mentions ''First few centimeters''.. So isn't this CIE's fault? Or is B the right answer too? Or is there something that i am missing?
Please someone help me. :/ If you understand what i am trying to say.
If the object is falling in a region without air resistance, then the acceleration of free-fall will be 10 m/s^2 till the moment the object hits the ground. It won't decrease to 0, and Terminal velocity won't be reached, since the object will continue to increase in speed at the rate of 10 m/s^2.
But, if an object falls in air resistance.. then the initial acceleration is 10 m/s^2.. but as its speed increases, the air resistance increases due to which the resultant force decreases and the acceleration decreases to 9, then to 8 and finally becomes zero when the weight and the air resistance become balanced. At this point terminal velocity is reached. Acceleration is zero.
If you look at the following MCQ from June 2006 paper 1..
The answer to this is C.
Now a small stone is falling from the top of the ladder.
They haven't mentioned if air resistance is present or not, but we can assume that it is.
Now the answer is C.. as it is the only logical explanation, but in C we can see that the gradient of the speed-time graph is constant..
Doesn't that mean there is a constant acceleration?
One thing we know for sure, is the distance of falling is very less, as it is falling from the top of a ladder.
It won't have time to reach terminal velocity, but isn't the acceleration supposed to decrease, even if only a little?
The stone will fall in a few seconds.. but still there is supposed to be an increase in speed, an increase in air resistance and a decrease in the acceleration.
But this graph shows clearly that there was no decrease in acceleration.
From this i formulated that whenever a question comes about a heavy object falling from a small distance above the ground, i should always assume that the acceleration will be constant 10 m/s^2 till the object hits the ground as it won't have enough time to increase in speed and thus increase the air resistance to decrease the acceleration.
Now, i recently encountered the following question in my exam, from May-June 2012 paper 1:
Now, in this question as you see, instead of the object falling in air, it is falling in thick oil.
We can assume that the same phenomenon takes place here, as it does when objects free fall in air..
The object will start to accelerate at 10 m/s^2 and gradually the acceleration will decrease.
But since i had finalized in the previous MCQ, the one posted before this one, that heavy objects (Stones, steel balls) accelerate at a constant rate in the first few seconds. Even if their acceleration decreases, it should be considered constant as the previous MCQ shows a straight line in the speed-time graph proving that there was a constant acceleration.
Now, this new question states ''During the first few CENTIMETERS''... it clearly mentions CENTIMETERS.
If the initial acceleration is 10 m/s^2 .. it can be visualized that within a second the steel ball would have traveled 10 m or 1000 cm.
And there would have been an increase in speed by 10 m/s..
But since it asks about the ''First few centimeters'' we can assume that they are talking about the first 10-20 cm maximum. That is a ''few''.. maybe even 5 cm.
Since, the acceleration was 10 m/s^2 in the start, it would have reduced by only a minute value in the first few centimetes.
I concluded in the previous question that heavy objects falling in the first few seconds, can be considered constant acceleration as the graph shows a straight line in the previous question. Implying the same concept here, keeping in mind they were talking about the ''First few centimeters''.. i thought that this can also be assumed to have constant acceleration in the first few seconds.. The first two options talk about Constant acceleration, but B says about constant accleration less than 10 m/s^2. Obviously it would be a little less than 10, so i selected B, based on the concept i had built in the previous MCQ which shows a straight line for the free-fall of a stone, before it hits the ground (Which would have taken seconds).
But the answer turns out to be C. ._.
Obviously, there would be a decrease in acceleration, OF COURSE.. but the previous MCQ shows a straight line.. and this new MCQ clearly mentions ''First few centimeters''.. So isn't this CIE's fault? Or is B the right answer too? Or is there something that i am missing?
Please someone help me. :/ If you understand what i am trying to say.
Whenever an object falls, the acceleration depends on the presence of air.
If the object is falling in a region without air resistance, then the acceleration of free-fall will be 10 m/s^2 till the moment the object hits the ground. It won't decrease to 0, and Terminal velocity won't be reached, since the object will continue to increase in speed at the rate of 10 m/s^2.
But, if an object falls in air resistance.. then the initial acceleration is 10 m/s^2.. but as its speed increases, the air resistance increases due to which the resultant force decreases and the acceleration decreases to 9, then to 8 and finally becomes zero when the weight and the air resistance become balanced. At this point terminal velocity is reached. Acceleration is zero.
If you look at the following MCQ from June 2006 paper 1..
The answer to this is C.
Now a small stone is falling from the top of the ladder.
They haven't mentioned if air resistance is present or not, but we can assume that it is.
Now the answer is C.. as it is the only logical explanation, but in C we can see that the gradient of the speed-time graph is constant..
Doesn't that mean there is a constant acceleration?
One thing we know for sure, is the distance of falling is very less, as it is falling from the top of a ladder.
It won't have time to reach terminal velocity, but isn't the acceleration supposed to decrease, even if only a little?
The stone will fall in a few seconds.. but still there is supposed to be an increase in speed, an increase in air resistance and a decrease in the acceleration.
But this graph shows clearly that there was no decrease in acceleration.
From this i formulated that whenever a question comes about a heavy object falling from a small distance above the ground, i should always assume that the acceleration will be constant 10 m/s^2 till the object hits the ground as it won't have enough time to increase in speed and thus increase the air resistance to decrease the acceleration.
Now, i recently encountered the following question in my exam, from May-June 2012 paper 1:
Now, in this question as you see, instead of the object falling in air, it is falling in thick oil.
We can assume that the same phenomenon takes place here, as it does when objects free fall in air..
The object will start to accelerate at 10 m/s^2 and gradually the acceleration will decrease.
But since i had finalized in the previous MCQ, the one posted before this one, that heavy objects (Stones, steel balls) accelerate at a constant rate in the first few seconds. Even if their acceleration decreases, it should be considered constant as the previous MCQ shows a straight line in the speed-time graph proving that there was a constant acceleration.
Now, this new question states ''During the first few CENTIMETERS''... it clearly mentions CENTIMETERS.
If the initial acceleration is 10 m/s^2 .. it can be visualized that within a second the steel ball would have traveled 10 m or 1000 cm.
And there would have been an increase in speed by 10 m/s..
But since it asks about the ''First few centimeters'' we can assume that they are talking about the first 10-20 cm maximum. That is a ''few''.. maybe even 5 cm.
Since, the acceleration was 10 m/s^2 in the start, it would have reduced by only a minute value in the first few centimetes.
I concluded in the previous question that heavy objects falling in the first few seconds, can be considered constant acceleration as the graph shows a straight line in the previous question. Implying the same concept here, keeping in mind they were talking about the ''First few centimeters''.. i thought that this can also be assumed to have constant acceleration in the first few seconds.. The first two options talk about Constant acceleration, but B says about constant accleration less than 10 m/s^2. Obviously it would be a little less than 10, so i selected B, based on the concept i had built in the previous MCQ which shows a straight line for the free-fall of a stone, before it hits the ground (Which would have taken seconds).
But the answer turns out to be C. ._.
Obviously, there would be a decrease in acceleration, OF COURSE.. but the previous MCQ shows a straight line.. and this new MCQ clearly mentions ''First few centimeters''.. So isn't this CIE's fault? Or is B the right answer too? Or is there something that i am missing?
Please someone help me. :/ If you understand what i am trying to say.
Remember to read the examiner reports first. It states:
"The movement of the ball falling through the oil is the same as that of a free-fall parachutist – the faster it goes, the greater is the resistant force."
As the resistance increases, the acceleration decreases.
The first question does not focus whether there is resistance or not as it solely asks about the speed if it is increasing, decreasing or is constant. If they had made curved graphs, it would have made the question a lot more confusing. The straight line graphs are just a general idea of the speeds and not the actual ones as the question does not focus about that.
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What I think is that in the 1st MCQ they have mentioned a small ball which means it has very less weight so me may assume that resistive forces are negligible therefore it undergoes a constant acceleration. While in the second MCQ, they have stated that it's a steel ball hence a greater weight and it is falling in thick oil means a greater resistance, so even in the first few centimetres acceleration starts to decrease. With the same explanation, I did the second MCQ in my exam and it happened to be correct. 
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What I think is that in the 1st MCQ they have mentioned a small ball which means it has very less weight so me may assume that resistive forces are negligible therefore it undergoes a constant acceleration. While in the second MCQ, they have stated that it's a steel ball hence a greater weight and it is falling in thick oil means a greater resistance, so even in the first few centimetres acceleration starts to decrease. With the same explanation, I did the second MCQ in my exam and it happened to be correct.
Even if in the first MCQ the stone was of little weight, it is supposed to experience decreasing acceleration.
Every object experiences that effect no matter what the weight.
The speed-time graph is supposed to show the decreasing acceleration through the decreasing gradient..
But in the first MCQ it shows a straight line, neglecting that entire concept.
I thought that since they are talking about a stone, it would fall to the ground in a matter of seconds, and the decrease in acceleration would be too less that it is being considered negligible and they are considering it to be constant acceleration.
So, applying the same concept in the second MCQ, where they are talking about a ''Few centimeters'' i thought that the steel ball would cover 10000 cm in one second due to its initial acceleration of 10 m/s^2, so in the first few centimeters the same concept as the previous MCQ can be applied, and the decrease in acceleration would be too minute, so can be considered negligible and thus constant. (As done by the previous MCQ graph)
Keeping in mind the straight line shown in the previous MCQ, and the ''First few centimeters'' in the second MCQ..
I selected option B in the second MCQ in my exam
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By making it ''easier'' they are neglecting the entire concept that the gradient of a speed-time graph represents the acceleration of an object.
There is no such thing as ''General'' or ''Actual'' speed-time graph. There is only one, and it should represent the acceleration as the gradient.
And i think this makes things more confusing, than actually showing the decreasing gradient, as students have that concept.
A straight line makes things more difficult and creates confusions. ._.
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I agree I was wrong with the first part but this is what is written in the book 'If the ball only falls a metre or so, it does not gain enough speed for air resistance to affect it's accleration sognificantly.'Even if in the first MCQ the stone was of little weight, it is supposed to experience decreasing acceleration.
Every object experiences that effect no matter what the weight.
The speed-time graph is supposed to show the decreasing acceleration through the decreasing gradient..
But in the first MCQ it shows a straight line, neglecting that entire concept.
I thought that since they are talking about a stone, it would fall to the ground in a matter of seconds, and the decrease in acceleration would be too less that it is being considered negligible and they are considering it to be constant acceleration.
So, applying the same concept in the second MCQ, where they are talking about a ''Few centimeters'' i thought that the steel ball would cover 10000 cm in one second due to its initial acceleration of 10 m/s^2, so in the first few centimeters the same concept as the previous MCQ can be applied, and the decrease in acceleration would be too minute, so can be considered negligible and thus constant. (As done by the previous MCQ graph)
Keeping in mind the straight line shown in the previous MCQ, and the ''First few centimeters'' in the second MCQ..
I selected option B in the second MCQ in my exam
I think the same concept could have been applied if they haven't mentioned the word 'steel ball' and 'thick oil' in the question.
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You are right about the first MCQ but you can't apply the same concept in the second one. And yeah it's writtn in the one by Stephen Pople, page 20, 1st paragrph.
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'If the ball only falls a meter or so, it does not gain enough speed for air resistance to affect it's acceleration significantly.'
And in that second MCQ, it said ''a few centimeters''..
Okay, in air resistance.. when two objects are falling, a paper and a steel ball...
The steel ball will accelerate and it will keep on increasing its speed, and since its weight is very large, a greater air resistance will be needed to balance its weight, and that greater air resistance can only be developed with a great speed, that it will have after a long time it has spent accelerating.
So, if a steel ball falls from a ladder, it will just hit the ground within a meter, so enough speed would not be gained and enough air resistance won't be there to cause its acceleration to be reduced. So we can say there was ''Constant acceleration''. Even though, the laws of Physics say that is not possible. Even if it is falling within a meter, there was a decrease in acceleration even if it was 0.0000000000001 m/s^2 decrease, but there was a decrease, due to the increase in air resistance.
But if a steel ball is thrown from like a million meters away, then it will keep on accelerating and its speed would keep on increasing, so would its air resistance, and eventually enough air resistance would be built to balance its huge weight, and a steel ball will reach terminal velocity too.
But a paper will reach terminal velocity faster, since it has a lesser weight, and lesser air resistance will be needed to balance that weight, and thus a lesser speed will need to be reached in order to build that air resistance, and that can happen quickly.
So, it can be concluded that a steel ball takes a longer time to reach terminal velocity, and thus it takes a longer time for its acceleration to decrease by a certain value, as compared to a paper. So in a few centimeters, there will a greater decrease in the acceleration of a light object like a paper, then it would be in a heavy object like a steel ball. A few centimeters is such a small quantity. The question specifically mentions ''Few centimeters''..
If a light stone was falling in thick oil, there would be a greater decrease in its acceleration in the same time, as it has a lesser weight and lesser water resistance is needed to balance it..
But in the case of steel ball, after travelling a long time, there will come a point when the water resistance will be equal to the weight..
That point might be 100's of meters away. All i thought was that in a ''few centimeters'' there won't be any significant change in its acceleration, and i remembered that previous MCQ, with a straight line showing acceleration of that stone, and that is why i selected B. :/
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That's really good to see you are so concerned about every single mark. Even I carlessly encirlced the wrong options and lost 2 marks in my exam and felt like killing my self afterwards but it was no use crying over the spilt milk.
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That's really good to see you are so concerned about every single mark. Even I carlessly encirlced the wrong options and lost 2 marks in my exam and felt like killing my self afterwards but it was no use crying over the spilt milk.
Same here. Lost 2 marks! :/
Both of them careless mistakes.
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Can anyone please tell me where can I get the past papers of Bio, physics and chemistry, the older ones I mean?
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Which year?
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May-June 2011 paper 11. Question 21, part c.
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Can anyone explain the Nitrogen Cycle in clear terms to me?
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Subject?May-June 2011 paper 11. Question 21, part c.
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Maths.
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It's pretty simple yar.The question states :What is the probability that Kelvin does not choose either black trousers or a red shirt
So we just have to remove the options in which he wears clothes that have either black trousers or a red shirt i.e combinations of BY,BR,GR(Gray trousers red shirt) are to be eleminated.
We are left with only option of Grey trouser yellow shirt which is 1/3 X 1/5 = 1/15
Understand?
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Not wearing Black Trouser OR Red Shirt.
They mentioned OR. Which means we have to eliminate the options in which he wears either a black trouser or a red shirt i.e that in which he wears a black trouser and a yellow shirt, and the one in which he wears a grey trouser and red shirt. The Black and Red can't be together as they mentioned in the question ''OR''. ._.
If they had said ''the probability of wearing NEITHER a Black trouser NOR a red shirt''.. then the logical option would be Grey Trouser and Yellow Shirt, since both Black AND Red are not to be included.
But they mentioned in the question ''EITHER and OR''..
Either means ONE OF THE TWO.
So the probability of wearing EITHER BLACK or RED SHIRT.. (Can't be both, since they used the words ''Either'' and ''Or'')
The following: BY, GR.. (Not BR, since they didn't say Black AND RED)
And the question said ''Probability of NOT wearing Either black or red''..
So, 1 - (probability of BY, GR)...
This should be right :/