How would you approach this question under timed conditions?

[ilovemcat]

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This question is taken from a TBR Physics passage. You really don't need to know what the passage is about since the question basically tells you all you need to know. The point of this post isn't to find an explanation for the question below, but instead to get an idea of how others approach problems, ie. how do they think through the problem to reach an answer (in a reasonable about of time ~1 min).


"A third experiment involved releasing an object from rest at the top of the incline, and then a short time later, releasing an object of the same mass from rest at the top of the same incline. What did Galileo find out about the distance between the two masses as they both rolled down the incline?"

A. The distance between the masses remained constant, since the acceleration acting on them was the same.
B. The distance between the masses increased, since the first mass accelerated at a greater rate.
C. The distance between the masses increased, since the acceleration acting on them was the same.
D. The distance between the masses decreased, since the acceleration caused the second mass to catch up with the first mass.



It would take about 20 seconds at least to read the question, understand what it's asking, and at least another 15 seconds to figure out a reasonable approach. It would take about 60 seconds to use that approach (if an equation is involved) and eventually chose an answer. (All together a time total of 1 1/2 min). However, if you instead read the question and then try to solve using some type of physics intuition, the answer would be solved in less time, but there's a chance your conceptual approach might be incorrect.

For me personally, I would of attempted to use intuition alone to save time. For example, I know that with increasing velocity, distance increases in a non-linear way. So the comparison becomes, what happens when comparing two falling objects that both increase non-linearly in distance. For some people this might seem obvious, but for me it was a blur. I mistakenly said that there wouldn't be a change in distance between them - that the distances between the masses remained constant. It's these types of mistakes that I encounter often.

If I instead used an alternative and more time consuming (math heavy approach), I could of used the appropriate equation and plugged in values. So in this case, that equation would be d = 1/2at^2. If you considered the 1/2a term to be 5, the only thing changing is t^2. So for t=1, d=5m then for t=2, d=20m, for t=3, d=45m. Then you can compare the distance between any two points like t=1 and t=2 (15m) and then t=2 to t=3 (25m). The distance between them is increasing.

Anyways, what this post boils down to is: For those of you scoring really well on practice tests, how would YOU typically approach a problem like this?

 

[NinjaMed]

This question is taken from a TBR Physics passage. You really don't need to know what the passage is about since the question basically tells you all you need to know. The point of this post isn't to find an explanation for the question below, but instead to get an idea of how others approach problems, ie. how do they think through the problem to reach an answer (in a reasonable about of time ~1 min).


"A third experiment involved releasing an object from rest at the top of the incline, and then a short time later, releasing an object of the same mass from rest at the top of the same incline. What did Galileo find out about the distance between the two masses as they both rolled down the incline?"

A. The distance between the masses remained constant, since the acceleration acting on them was the same.
B. The distance between the masses increased, since the first mass accelerated at a greater rate.
C. The distance between the masses increased, since the acceleration acting on them was the same.
D. The distance between the masses decreased, since the acceleration caused the second mass to catch up with the first mass.



It would take about 20 seconds at least to read the question, understand what it's asking, and at least another 15 seconds to figure out a reasonable approach. It would take about 60 seconds to use that approach (if an equation is involved) and eventually chose an answer. (All together a time total of 1 1/2 min). However, if you instead read the question and then try to solve using some type of physics intuition, the answer would be solved in less time, but there's a chance your conceptual approach might be incorrect.

For me personally, I would of attempted to use intuition alone to save time. For example, I know that with increasing velocity, distance increases in a non-linear way. So the comparison becomes, what happens when comparing two falling objects that both increase non-linearly in distance. For some people this might seem obvious, but for me it was a blur. I mistakenly said that there wouldn't be a change in distance between them - that the distances between the masses remained constant. It's these types of mistakes that I encounter often.

If I instead used an alternative and more time consuming (math heavy approach), I could of used the appropriate equation and plugged in values. So in this case, that equation would be d = 1/2at^2. If you considered the 1/2a term to be 5, the only thing changing is t^2. So for t=1, d=5m then for t=2, d=20m, for t=3, d=45m. Then you can compare the distance between any two points like t=1 and t=2 (15m) and then t=2 to t=3 (25m). The distance between them is increasing.

Anyways, what this post boils down to is: For those of you scoring really well on practice tests, how would YOU typically approach a problem like this?

I just used POE, and the first one is wrong. Second one is wrong, and looking at the fourth answer, it would also have to be wrong. Is the third one the correct one? It's not the t-method, but the reasoning in ctr 1 of tbr. I kinda just modified it for POE. The first step I did was visualize the two "spheres" rolling down the inclined plane, next my gut kept telling me to look for time. Time was the key here in the POE. It was just instinct to look there for some reason, I can't explain it.

 

[PiBond]

This question is taken from a TBR Physics passage. You really don't need to know what the passage is about since the question basically tells you all you need to know. The point of this post isn't to find an explanation for the question below, but instead to get an idea of how others approach problems, ie. how do they think through the problem to reach an answer (in a reasonable about of time ~1 min).


"A third experiment involved releasing an object from rest at the top of the incline, and then a short time later, releasing an object of the same mass from rest at the top of the same incline. What did Galileo find out about the distance between the two masses as they both rolled down the incline?"

A. The distance between the masses remained constant, since the acceleration acting on them was the same.
B. The distance between the masses increased, since the first mass accelerated at a greater rate.
C. The distance between the masses increased, since the acceleration acting on them was the same.
D. The distance between the masses decreased, since the acceleration caused the second mass to catch up with the first mass.



It would take about 20 seconds at least to read the question, understand what it's asking, and at least another 15 seconds to figure out a reasonable approach. It would take about 60 seconds to use that approach (if an equation is involved) and eventually chose an answer. (All together a time total of 1 1/2 min). However, if you instead read the question and then try to solve using some type of physics intuition, the answer would be solved in less time, but there's a chance your conceptual approach might be incorrect.

For me personally, I would of attempted to use intuition alone to save time. For example, I know that with increasing velocity, distance increases in a non-linear way. So the comparison becomes, what happens when comparing two falling objects that both increase non-linearly in distance. For some people this might seem obvious, but for me it was a blur. I mistakenly said that there wouldn't be a change in distance between them - that the distances between the masses remained constant. It's these types of mistakes that I encounter often.

If I instead used an alternative and more time consuming (math heavy approach), I could of used the appropriate equation and plugged in values. So in this case, that equation would be d = 1/2at^2. If you considered the 1/2a term to be 5, the only thing changing is t^2. So for t=1, d=5m then for t=2, d=20m, for t=3, d=45m. Then you can compare the distance between any two points like t=1 and t=2 (15m) and then t=2 to t=3 (25m). The distance between them is increasing.

Anyways, what this post boils down to is: For those of you scoring really well on practice tests, how would YOU typically approach a problem like this?

I eliminate B and D first because acceleration of the masses is the same. I pick C because I know that, even though two objects have the same acceleration, the one that's been accelerating for a longer time will have a great velocity (and continues to) and be "pulling away" from the second mass despite there same acceleration.

 

[ilovemcat]

I eliminate B and D first because acceleration of the masses is the same. I pick C because I know that, even though two objects have the same acceleration, the one that's been accelerating for a longer time will have a great velocity (and continues to) and be "pulling away" from the second mass despite there same acceleration.

Why couldn't I think of it that way, lol. That makes more sense though.

 

[ilovemcat]

I just used POE, and the first one is wrong. Second one is wrong, and looking at the fourth answer, it would also have to be wrong. Is the third one the correct one? It's not the t-method, but the reasoning in ctr 1 of tbr. I kinda just modified it for POE. The first step I did was visualize the two "spheres" rolling down the inclined plane, next my gut kept telling me to look for time. Time was the key here in the POE. It was just instinct to look there for some reason, I can't explain it.

Yep, choice C is the correct answer. To do POE though, you have to use some conceptual approach. I'm guessing you either realized that distance isn't linear or like PiBond, that velocity is moving faster and faster each second (pulling away further and further).

 

[NinjaMed]

Yep, choice C is the correct answer. To do POE though, you have to use some conceptual approach. I'm guessing you either realized that distance isn't linear or like PiBond, that velocity is moving faster and faster each second (pulling away further and further).

I realized that the biggest factor was time. It was mentioned in the question, "a short time later." It gave the first sphere the advantage. The first sphere would reach a higher velocity sooner, and it became a race thereafter which the second sphere could not win. I used the Raging POM approach to POE. And it basically calls to get angry at everyone wrong answer and it also forces speed in tackling the questions and eliminating the wrong answers. It is also partly physiology as well, kinda gets me like I am being hit in the face by the question, and I HATE being punched in the face. Punch my chin? Sure, go for a knock-out, and try to win a fight against me? No problem! But punch my face? All bets are off! 😡😡😡

 

[ridethecliche]

I drew 2 v/t graphs in my head and shifted one of them over to the right to indicate that object 2 started later.

So object 1's v was higher at every point relative to object 2. Area under the curve was always greater as well. So, distance between the 2 was increasing even though they were accelerating the same.

For me, it was to think about the fact that 2 things with the same acceleration have the same velocity if they start from 0, but if there's a lag in time then one gets a 'head start' and the other is already moving faster. So more V= more D.

 

[ridethecliche]

I realized that the biggest factor was time. It was mentioned in the question, "a short time later." It gave the first sphere the advantage. The first sphere would reach a higher velocity sooner, and it became a race thereafter which the second sphere could not win. I used the Raging POM approach to POE. And it basically calls to get angry at everyone wrong answer and it also forces speed in tackling the questions and eliminating the wrong answers. It is also partly physiology as well, kinda gets me like I am being hit in the face by the question, and I HATE being punched in the face. Punch my chin? Sure, go for a knock-out, and try to win a fight against me? No problem! But punch my face? All bets are off! 😡😡😡

Have you considered alternate career choices?

Motivational speaking for one.

😉

 

[ilovemcat]

I realized that the biggest factor was time. It was mentioned in the question, "a short time later." It gave the first sphere the advantage. The first sphere would reach a higher velocity sooner, and it became a race thereafter which the second sphere could not win. I used the Raging POM approach to POE. And it basically calls to get angry at everyone wrong answer and it also forces speed in tackling the questions and eliminating the wrong answers. It is also partly physiology as well, kinda gets me like I am being hit in the face by the question, and I HATE being punched in the face. Punch my chin? Sure, go for a knock-out, and try to win a fight against me? No problem! But punch my face? All bets are off! 😡😡😡

Looool, you lost me at the end.

I drew 2 v/t graphs in my head and shifted one of them over to the right to indicate that object 2 started later.

So object 1's v was higher at every point relative to object 2. Area under the curve was always greater as well. So, distance between the 2 was increasing even though they were accelerating the same.

For me, it was to think about the fact that 2 things with the same acceleration have the same velocity if they start from 0, but if there's a lag in time then one gets a 'head start' and the other is already moving faster. So more V= more D.

That's actually an interesting approach to use.

Looking at several of the questions in TBR passages, I noticed a lot could be answered based on some type of intuition. I wonder how similar this is to the recent MCAT.

 

[Rabolisk]

It took me 50 seconds conceptually. Don't worry about time. I've never had trouble finishing PS section, and you won't either. I probably would have returned to this question and done some calculations to convince myself.

 

[ilovemcat]

It took me 50 seconds conceptually. Don't worry about time. I've never had trouble finishing PS section, and you won't either. I probably would have returned to this question and done some calculations to convince myself.

Yeah, the timer really throws my game off. I like to approach problems by first thinking of it conceptually... arriving at an answer, then using some kind of math approach to confirm it. Because of timing though, you really don't have that leisure to do both (unless you had time left at the end). I think that's the reason why a lot of people walk out of the exam not feeling confident with their performance. Hopefully though with more practice, I'll learn to work with the clock instead of racing against it.

Thanks for the replies everyone. This was helpful.

 

[ridethecliche]

The number 1 rule of any physics problem you can't think about in your head is to draw it out.

Honestly, just think things through for a second instead of jumping to the formula. Blindly jumping to a formula can throw you off if you have to apply it 'differently'.

You would have been safe here though.

I used to race bikes, so I thought of chasing someone downhill. There are other factors at play, but if someone has a head start, you have to work hard to catch them even if they're just coasting. I.e. you have to accelerate harder than they are.

Same thing on flat ground. If you're accelerating at the same speed as someone who has a head start, you'll never catch them and their velocity will always be higher than you.

This isn't a question about gravity, hills, or rolling. It's a question JUST about acceleration.

 

[ModusProbandi]

This question is taken from a TBR Physics passage. You really don't need to know what the passage is about since the question basically tells you all you need to know. The point of this post isn't to find an explanation for the question below, but instead to get an idea of how others approach problems, ie. how do they think through the problem to reach an answer (in a reasonable about of time ~1 min).


"A third experiment involved releasing an object from rest at the top of the incline, and then a short time later, releasing an object of the same mass from rest at the top of the same incline. What did Galileo find out about the distance between the two masses as they both rolled down the incline?"

A. The distance between the masses remained constant, since the acceleration acting on them was the same.
B. The distance between the masses increased, since the first mass accelerated at a greater rate.
C. The distance between the masses increased, since the acceleration acting on them was the same.
D. The distance between the masses decreased, since the acceleration caused the second mass to catch up with the first mass.

I choose C.

 

[Graffiti]

I drew 2 v/t graphs in my head and shifted one of them over to the right to indicate that object 2 started later.

So object 1's v was higher at every point relative to object 2. Area under the curve was always greater as well. So, distance between the 2 was increasing even though they were accelerating the same.

For me, it was to think about the fact that 2 things with the same acceleration have the same velocity if they start from 0, but if there's a lag in time then one gets a 'head start' and the other is already moving faster. So more V= more D.

maybe i'm wrong, but wouldn't drawing it that way mislead you into thinking that the distance is constantly changing? atleast thats how im picturing it right now.

 

[ridethecliche]

maybe i'm wrong, but wouldn't drawing it that way mislead you into thinking that the distance is constantly changing? atleast thats how im picturing it right now.

The distance is changing 😉

 

[Bayonetwork]

Read question and skim answers for concepts/common variables I need to apply.
(less than 30 seconds)

I use POE to eliminate B and D right away knowing that acceleration of two equally massed objects down the same incline is the same. ( 10 seconds)

Then I think about distance and time in regards to A and C. I think of dropping two same objects off of a building 2 seconds apart. This means that the first object will land and 2 seconds later the second one will since displacement, acceleration and final velocity are all the same. Since final velocity is greater than initial velocity the only way the objects hit 2 seconds apart is if they are further apart from each other when they land.
(less than 30 seconds)

Total time is 1 minute or less.