Having a problem with TBR Physics

[Vanguard23]

OK, I've gone over TBR Chemistry a bit. Love it. But the Physics Sections I-III so far are starting to irk me.
Here are some example:
From Sec. III(Torques and Momentum):
Passage I:
Question 1: What is the approximate speed of the center of mass of the child/sled system, after the collision.
The Answer? 1m/s.
Now this would be fine except the passage makes it very ambigious given a child runs into a sled, then into a log(two collisions) yet the question makes no distinction of what collision it is refering to.

Passage II:
Question 9:Applying a force parallel to a lever arm will:
I chose "No effect". It makes sense. You're pressing into the torque arm.
The Answer? May produce a translational motion, but will not produce a rotational motion.
I'm sorry, but this is a bit of a cop-out. Yeah, sure, it MIGHT produce translational motion if you break the bolt in half. How the hell are we supposed to take into considering highly unlikely events if this is a test that typically brushes such details aside?

Question 10:
It asks for the equation of the torque arm for a ball acting on a rod. Now, I've been through torques left and right and I assumed it'd be Lmgsin theta(after all, gravity is acting in the vertical direction). I also used Nova's physics and they almost always use sin.
The Answer? Lmgcos theta. What the hell? The explanation in the back of the book is ridiculous, as well. It asks what would happen if you turned the rod vertically and what would the torque be? Zero. This is what cosine is at that point. But that doesn't make sense to me regarding the question since I've always used sin given it's perpendicular to most torque arms.

There's a few more in the first section( I just outrightly skipped the second section) that were similar to the first two example I gave. They took the smallest little detail or even contradiction all together and used it to make the most logical choice wrong, or make their "correct" answer choices all together inconsistent.
I'm not using the book to learn the minute little nit-picks that they can squeeze out of a question stem. I'm using it to learn concepts and gain intuition about answering questions. Sadly, it seems to be aiming sort of for the former.
Anyone else feel the same?

edit: You know what? I give up on TBR Physics. I just did the third passage and one of the questions was such:
An astronaut on a spacewalk throws a ball at a box and undergoes an inelastic collision. How far is the ball/box system after time T?
I thought it was the original distance of the box from the astronaut + (T) times the velocity of the ball/box system.
The answer? The above and then some. Why? Conservation of momentum. The astronaut gets thrown back some. Well, ok, he's on a spacewalk, but there's no information about him other than that. How do we know he's floating about in space instead of on the hull of something like a massive space shuttle or station and hence his delta v would be absolutely negligble(if at all existent)?

It's little things like that which are pissing me off about TBR. I give up on it. I'm not trying to learn physics with *their* exceptions/contradictions to the rules in place. I'm trying to learn concepts and all this is doing is confusing me. I'll go back to Nova's; at least any exceptions that they put in place are a little more reasonable.

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[BerkReviewTeach]

OK, I've gone over TBR Chemistry a bit. Love it. But the Physics Sections I-III so far are starting to irk me.
Here are some example:
From Sec. III(Torques and Momentum):
Passage I:
Question 1: What is the approximate speed of the center of mass of the child/sled system, after the collision.
The Answer? 1m/s.
Now this would be fine except the passage makes it very ambigious given a child runs into a sled, then into a log(two collisions) yet the question makes no distinction of what collision it is refering to.

Passage II:
Question 9:Applying a force parallel to a lever arm will:
I chose "No effect". It makes sense. You're pressing into the torque arm.
The Answer? May produce a translational motion, but will not produce a rotational motion.
I'm sorry, but this is a bit of a cop-out. Yeah, sure, it MIGHT produce translational motion if you break the bolt in half. How the hell are we supposed to take into considering highly unlikely events if this is a test that typically brushes such details aside?

Question 10:
It asks for the equation of the torque arm for a ball acting on a rod. Now, I've been through torques left and right and I assumed it'd be Lmgsin theta(after all, gravity is acting in the vertical direction). I also used Nova's physics and they almost always use sin.
The Answer? Lmgcos theta. What the hell? The explanation in the back of the book is ridiculous, as well. It asks what would happen if you turned the rod vertically and what would the torque be? Zero. This is what cosine is at that point. But that doesn't make sense to me regarding the question since I've always used sin given it's perpendicular to most torque arms.

There's a few more in the first section( I just outrightly skipped the second section) that were similar to the first two example I gave. They took the smallest little detail or even contradiction all together and used it to make the most logical choice wrong, or make their "correct" answer choices all together inconsistent.
I'm not using the book to learn the minute little nit-picks that they can squeeze out of a question stem. I'm using it to learn concepts and gain intuition about answering questions. Sadly, it seems to be aiming sort of for the former.
Anyone else feel the same?

edit: You know what? I give up on TBR Physics. I just did the third passage and one of the questions was such:
An astronaut on a spacewalk throws a ball at a box and undergoes an inelastic collision. How far is the ball/box system after time T?
I thought it was the original distance of the box from the astronaut + (T) times the velocity of the ball/box system.
The answer? The above and then some. Why? Conservation of momentum. The astronaut gets thrown back some. Well, ok, he's on a spacewalk, but there's no information about him other than that. How do we know he's floating about in space instead of on the hull of something like a massive space shuttle or station and hence his delta v would be absolutely negligble(if at all existent)?

It's little things like that which are pissing me off about TBR. I give up on it. I'm not trying to learn physics with *their* exceptions/contradictions to the rules in place. I'm trying to learn concepts and all this is doing is confusing me. I'll go back to Nova's; at least any exceptions that they put in place are a little more reasonable.

From what I read here, your physics knowledge is solid, so whatever you do to review in terms of content will work to consolidate the information. But be careful before you write some of these questions off, because that is what will get you ready for the MCAT more than knowing facts and equations. The questions aren't as random as they may appear at your first glance and the ambiguity you mention is crucial in terms of your preparation for the real MCAT. If you figure out why the seemingly ambiguous questions are actually not ambiguous (which you usually need to do POE on the answer choices to see), then you will be so much better off for your real MCAT.

Consider Question 1: You are correct that there are two collisions. For the first collision a 24-kg kid going 1.8 m/s strikes a stationary 18-kg sled, so the combined final mass is slightly less than double the initial mass, making the final speed slightly more than half of the initial speed. That makes 1.0 m/s the only candidate of the choices. If you consider the second collision, then you'll see a 42-kg combined child-sled system collides with a stationary 50-kg log, resulting in a little more than double the mass and thus a final speed following the second collision of just less than 0.5 m/s (half of 1.0 m/s). 0.5 is not listed as a choice but 1.0 is, so the question can only be referring to the first collision. This sort of logic is definitely fair game for the MCAT and POE can be done quickly if you trust your intuition. You can learn a great deal from answering your own question here of "how do I know which collision they are talking about?" They could be talking about either one, but only one of the numerical choices fits for either collision.

Consider Question 9: You need to be careful on questions like this that you don't zero your mental image in on a system with a bolted fulcrum. No where in the question or passage does it mention such a system (with an anchored fulcrum), although a picture in the previous question for a system specific to that question shows a wrench and a bolt. You have created a mental image of a bolt at the fulcrum. In this question, they asking generally what a parallel force can do. It cannot produce a torque, so B and D are gonzo. However, a parallel force definitely can produce translational motion if there is no opposing force (such as static friction, etc...). Just because the chapter is on torque doesn't mean all of the questions are going to exclusively consider torque and no other aspects of physics. The questions are designed to incorporate several topics tied in with the topic at hand, because the MCAT mixes topics in their passages and questions.

Consider Question 10: This is designed with a VERY specific goal in mind and that is to force the student to consider the system as shown, not as memorized. You are 100% correct that the torque is found by multiplying force by lever arm and sine of the angle between the lever arm and applied force. But if you look at the picture in the drawing, you'll note that the angle shown is not the angle between the applied force and lever arm, but is instead the angle between the plank and the horizontal. The angle specified in the picture is the other non-90-degree angle in the triangle associated with the diagram. Trig tells us that it is the angle shown is the complimentary angle of the angle between the force vector and moment arm. If you recall, sine of one non-90 angle will equal the cosine of the other non-90 angle in the right triangle, so in essence, the sin theta you have memorized is equal to cosine phi (where phi is the other non-90 angle). This is not only a reasonable scenario for a question, but one that is common in physics and completely fair game for an MCAT question. The point to this question is that you can't just blindly memorize equations. The MCAT is a thinking exam, and this question makes you think. The answer explanation addresses both the trig solution as well as an intuition solution where you consider the extreme cases of horizontal and vertical. This is actually a very powerful technique when coupled with POE.

I don't deny that about 10% of the questions in the physics books make you want to swear, but please realize that these are the ones where you gain the most intution and/or speed. Hang in there and keep working through the pisser questions, because in the end they'll make you a more conceptual physics student.

As for the spacewalk question, space walk is all you need to know. Walking in space is floating (or free falling with the objects around you). You HAVE to know that recoil applies in that situation, because that is the crux of the question. Be careful not to add the conditions of your mental image to the question presented. If there was a wall, then they wouldn't be space walking. As it stands in a free floating system, if you push an object to the right, then you recoil to the left and end up a distance apart that depends on both your motion and the object's motion. That is actually an excellent and highly typical question.

Just fight through the occassional pisser questions, because questions like the space walking questions are exactly what you need to study. It tests a common physics concept in an atypical way that requires you to think and know your definitions, exactly what will be true on the actual MCAT. Good luck and keep your nose to the grindstone!

 

[Vanguard23]

Ok, thanks for that long explanation. I have some nit-picks but they're only that.
My main beef is that there really isn't any explanations(like you provided) so I'm left hanging with what appears to be contradictions with little way of explaining discrepancies. That can be very counter-productive.

I'm still having trouble with that torque arm problem. How can I tell when to use sin and when to use cos? Because the angle is always at that position anyways.