#145 Examkrackers 1001 physics

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A man pushes horizontally on a block at rest. Which of the following is true?

A. Newton's 3rd Law dictates that the block experiences a force equal and opposite to the pushing force.

B. Newton's 1st Law dictates that in the absence of any other forces, the block will remain at rest.

C. Regardless of other forces that may be acting on the block, the acceleration of the block will be inversely proportional to its mass.

D. Newton's 3rd Law dictates that an equal and opposite force will cancel the pushing force and the block will not move.

Correct answer is C.

I ruled out C off the bat, because to me, "inversely proportional" designates that there is a constant present. So, either the Force would have to be constant, which it is not ("Regardless of other forces"). After all, when a is inversely proportional to b, if you multiply a by 5, then b is multiplied by the reciprocal (1/5). Thus, I marked B, because I assumed that perhaps the man's force had not overcome static friction. C simply did not make sense!

So, my question is: is my definition of "inversely proportional" incorrect for physics? Is there an assumption that I'm not seeing here? If the "Regardless of other forces" were not there, I would most likely have marked C, because the force would be constant. Or, if the answer had been phrased "Regardless of other forces, the acceleration of the block will be directly proportional to the Force" because mass, unlike force, is reasonable to assume as a constant.

I know it seems like I am over thinking this, but when answering the question, I didn't overthink it. I just ruled C out because the force could not be taken as a constant!! How can I avoid doing that on the MCAT? I find the wording to be really ambiguous in much of the physical sciences.

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A man pushes horizontally on a block at rest. Which of the following is true?

A. Newton's 3rd Law dictates that the block experiences a force equal and opposite to the pushing force.

B. Newton's 1st Law dictates that in the absence of any other forces, the block will remain at rest.

C. Regardless of other forces that may be acting on the block, the acceleration of the block will be inversely proportional to its mass.

D. Newton's 3rd Law dictates that an equal and opposite force will cancel the pushing force and the block will not move.

Correct answer is C.

I ruled out C off the bat, because to me, "inversely proportional" designates that there is a constant present. So, either the Force would have to be constant, which it is not ("Regardless of other forces"). After all, when a is inversely proportional to b, if you multiply a by 5, then b is multiplied by the reciprocal (1/5). Thus, I marked B, because I assumed that perhaps the man's force had not overcome static friction. C simply did not make sense!

So, my question is: is my definition of "inversely proportional" incorrect for physics? Is there an assumption that I'm not seeing here? If the "Regardless of other forces" were not there, I would most likely have marked C, because the force would be constant. Or, if the answer had been phrased "Regardless of other forces, the acceleration of the block will be directly proportional to the Force" because mass, unlike force, is reasonable to assume as a constant.

I know it seems like I am over thinking this, but when answering the question, I didn't overthink it. I just ruled C out because the force could not be taken as a constant!! How can I avoid doing that on the MCAT? I find the wording to be really ambiguous in much of the physical sciences.

F=ma so a=F/m. That's the definition of inversely proportional. Remember that the F is really the "sum of all forces" and you'll be alright.
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A, B and D are blatantly wrong - you should never choose any of these. C is very poorly worded, since you cannot tell much about the acceleration if you vary both mass and net force and "regardless of other forces" pretty much guarantees that the net forces is not constant. What I think they were trying to say is "If other forces are disregarded...".
 
After first reading the question I canceled out B because the question says the guy is pushing the block, so there is a force. Otherwise I would have thought of B as a possible answer.
 
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F=ma so a=F/m. That's the definition of inversely proportional. Remember that the F is really the "sum of all forces" and you'll be alright.
Sent from my SGH-T999 using SDN Mobile

definition from mathwords.com: A relationship between two variables in which the product is a constant. When one variable increases the other decreases in proportion so that the product is unchanged.

Sorry, I simply can't think like you're telling me to think. I know what inversely proportional means, unless inversely proportional is used differently in the physics context. You can't tell me that m and a are inversely proportional because the mass does not go down as the acceleration goes up and vice versa, if the force does not remain constant. Not to mention that mass is not an immutable property, and since changing/replacing the block isn't mentioned, it just seems wrong. They are related inversely by an equation but are not "inversely proportional" because the force is not assumed to be constant.
 
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A, B and D are blatantly wrong - you should never choose any of these. C is very poorly worded, since you cannot tell much about the acceleration if you vary both mass and net force and "regardless of other forces" pretty much guarantees that the net forces is not constant. What I think they were trying to say is "If other forces are disregarded...".

I guess... but, there are questions on the MCAT that will also be badly worded. How should one approach badly worded questions and answers? Any advice? In my mind, I could better justify B by assuming that the force maybe had not over come static friction, since the man was applying the force to a block at rest. I literally could not justify any of them, and dismissed C right off the bat, but B just seemed the least wrong because of its vagueness.
 
I guess... but, there are questions on the MCAT that will also be badly worded. How should one approach badly worded questions and answers? Any advice? In my mind, I could better justify B by assuming that the force maybe had not over come static friction, since the man was applying the force to a block at rest. I literally could not justify any of them, and dismissed C right off the bat, but B just seemed the least wrong because of its vagueness.

There is no way that B can be correct - you are given that there is exactly one force on it, the person pushing on it and nothing else. Under these conditions there is no way for the block to stay stationary.

I have not taken the MCAT but based on previous discussions about similar poorly designed questions, the MCAT is well written and you won't have to deal with too much of this type of ambiguity. Someone with more experience should be able to confirm that. I would not lose sleep over one messed up question by any of the prep companies.
 
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