Physics Questions

NS_Tutor_Andrew
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Re: Physics Questions

Post by NS_Tutor_Andrew » Mon Mar 19, 2018 6:35 pm

Hi MCAT_Retaker,

Thank you for the questions! Yes, about the question on pg. 75, "skater 2" comes from Test 2.

For Q2 in chapter 4, we need to go to the passage to figure out what contributes to thermal injury. We're told that "Thermal injury risk increases when the cooling required to maintain thermal equilibrium exceeds the heat loss to the environment." A and D pretty clearly fall within the domain of features that would increase the amount of heat the body is receiving, therefore increasing the cooling needed to maintain thermal equilibrium, which all things being equal increases the risk of thermal injury. C can be eliminated because higher humidity makes it harder for the body to cool itself. This leaves skin thickness. Equation 1 tells us that Q/t (the rate of heat lost to the environment) has an inverse relationship with skin thickness, meaning that increased skin thickness reduces heat loss to the environment, which also should make it harder for the body to cool itself. It looks like there is a typo here and that B should read "decreased skin thickness" to be a correct answer to this NOT question. We will make a note to fix that for future editions -- the key takeaway point here is to understand the logic connecting Equation 1 to heat loss and thermal injury.
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Re: Physics Questions

Post by MCAT_Retaker » Sat Mar 31, 2018 10:30 pm

For writing out the acceleration, somehing I got when I took the class a couple years ago and now forgot some of it, I always thought of it as the equation, shown in the second picture. Your M2g (weight) is being pulled down, with your m1g (weight of 1) and friction force is oppsed. From the block 2's perspective, i dont even account the tension, jsut the weight of it going down as positive. Is this also a good way to look at it?
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MCAT_Retaker
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Re: Physics Questions

Post by MCAT_Retaker » Sat Mar 31, 2018 10:51 pm

Also in these equations, what does the second second sin equation mean, V 0 Sin theta? = vyi????
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Re: Physics Questions

Post by MCAT_Retaker » Sun Apr 01, 2018 1:35 am

In this case, I alwas get confused on the distance. the distance in torque is always from the pivot point right? , not neessary from the fulcrum? because in this case the toes are the fulcrum, but thats not where r comes from

for the last distance calculated, i would have made it 16 cm. instead of 4.
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NS_Tutor_Andrew
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Re: Physics Questions

Post by NS_Tutor_Andrew » Tue Apr 03, 2018 5:42 pm

Hi MCAT_Retaker,

Taking these questions in order:

Re: the mass on an inclined plane + pulley, it sounds like you're asking whether you can/should skip over the step of explicitly referring to the force of tension? If so, the answer is "kind of" -- if you can recognize that m2 falling is going to be counterbalanced by m1 & friction, then that might be simpler and applicable in many problem-solving situations. However, a question *can* ask directly about tension, in which case you may need to recognize how the string functions to "transmit" those forces.

V0sin(θ) = V_yi means that the initial y-component of velocity is equal to the magnitude of the initial velocity * sin(θ).

Re: torque, you do want to look for the distance to the fulcrum (see here) and based on the diagram, it does seem like they're focusing on a fulcrum in the ankle, although that might be tough to see, because the potential rotation posterior to the ankle isn't actually happening due to the upward force that the Achilles tendon is exerting.

Hope this helps clarify those questions!
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Re: Physics Questions

Post by MCAT_Retaker » Wed Apr 11, 2018 4:24 am

can you please give a quick further analysis as to why question 3(passage pased), from chapter 5 is B.
The force of gravity acting on the bulb is greater than the buoyant force acting on the bulb.

Also this passage, how do we know the temp of the ethanol?
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Re: Physics Questions

Post by NS_Tutor_Andrew » Sat Apr 14, 2018 7:25 pm

Hi MCAT_Retaker,

Re: the temperature, Fig. 1 gives you information for various temperatures, and the Q stem should always specify the temperature. For question 3, this question is getting at the idea that there is a pressure differential between the top and bottom of the bulb, but I think it makes a subtle error by not recognizing that the buoyant force is actually due to pressure.

Hope this helps clarify your question!
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Re: Physics Questions

Post by MCAT_Retaker » Sat Apr 14, 2018 9:39 pm

Thank you. sorry for all my questions. but I really appreciate it. For Chapter 7 question 2, it's like a puzzle. I would have never known to decodne the digits like that. is that normal?

Also for question 1 on that passage, can you intutiively explain what the true current is vs the measured.

for question 7 on the independent, you cannot use P=V^2/R. becuase the voltage isnt for one resistor right?
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Re: Physics Questions

Post by NS_Tutor_Andrew » Tue Apr 17, 2018 4:52 pm

Hi MCAT_Retaker,

Please don't apologize, we're happy to help!

Re: Q2 in chapter 7, I wouldn't say it's typical in the sense that you're super-likely to see a question asked in exactly that way. But there are some AAMC questions about circuits that feel like logic puzzles in a broadly similar way, so I think it's decent practice.

We've gotten a fair amount of questions about Q1 (true vs. measured resistance). Underlyingly, the idea is that any measurement might only approximate the true value, and that one reason for this can be if the underlying mechanics of the tool used to measure a value interferes with the system you're measuring. In this case, an ideal multimeter would draw no resistance, allowing perfect measurements of the circuit, but in reality, it does have some resistance, meaning that it becomes part of the circuit system. Therefore, the measured value of the current is not going to be equal to the true value. As a very crude analogy, imagine that you want to know the temperature of a fresh pizza in a sealed box. You open up the box, sample the pizza, and measure the temperature. However, the pizza sample will almost certainly lose heat as you transfer it to wherever you measure the temperature. Thus, the measured temperature will not equal the "true" temperature. The mechanisms of these situations are different, but hopefully that illustrates the issue.

For Q7, you actually could use P = V2/R, but you'd have to make sure to use V for each specific resistor, not for the system as a whole -- so that would be 5 V, not 15 V. If you do so, P = 5^2 V/5 ohms = 5 W. The explanation instead solves it for the whole system and then breaks it down to find the value for each resistor. Either way works here, you just have to be careful about which methods you use.

Hope this helps!!
Andrew D.
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Re: Physics Questions

Post by MCAT_Retaker » Wed May 30, 2018 7:23 pm

Can you elaborate on question 4 from the Physics Content Review Book. Chapter 9- the passage. Page 224. The diffraction experiment passage.
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