Physics question thread

[Shrike]

All users may post questions about MCAT and OAT physics here. We will answer the questions as soon as we reasonably can. If you would like to know what physics topics appear on the MCAT, you should check the MCAT Student Manual (http://www.aamc.org/students/mcat/studentmanual/start.htm), though be warned, there are subjects listed there that are rarely tested, or that appear in passages only and need not be learned.

Be sure to check the Physics FAQs and Topic Writeups thread if you have a general question; eventually, many of your answers will be located there. Also, a request: to keep this thread at least somewhat neat, when replying to someone else's post please refrain from quoting anything more than what's necessary for clarity.

Acceptable topics:

• general, MCAT-level physics
• particular MCAT-level physics problems, whether your own or from study material
• what you need to know about physics for the MCAT
• how best to approach to MCAT physics passages
• how best to study MCAT physics
• how best to tackle the MCAT physical sciences section

Unacceptable topics:

• actual MCAT questions or passages, or close paraphrasings thereof
• anything you know to be beyond the scope of the MCAT

Side note: anyone who knows how to post subscripts and superscripts in this system, please PM me the method. I also wouldn't mind knowing how to post some obvious symbols, such as Greek letters and an infinty sign. Should be a matter of changing fonts, but I don't know what's available; again, a PM would be appreciated.

If you really know your physics, I can use your help. If you are willing to help answer questions on this thread, please let me know. Here are the current official contributors to the this thread -- a team to which I hope to add more people:

Thread moderated by: Shrike. Shrike is a full-time instructor for The Princeton Review; he has taken the MCAT twice for no good reason, scoring 14 on the physical sciences section each time. He majored in mathematics, minored in physics, and spent several years accumulating unused school experience (in economics and law).

Also answering questions: Xanthines, a Kaplan instructor. He scored 13 on the PS section of the MCAT and 34 overall.

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[dill_punjabi]

Q 86: Which of the follwoing represents the maximum hieght h reached by the projectile?
A v2/2g
B 1/8 g t^2
C vt
D. vtsin(x)

Answer B, I m confused that why are they ignoring initial velocity in B. If I use Distance formula then answer should be = vsin(x)t+1/8gt^2

 

[BrokenGlass]

Q 86: Which of the follwoing represents the maximum hieght h reached by the projectile?
A v2/2g
B 1/8 g t^2
C vt
D. vtsin(x)

Answer B, I m confused that why are they ignoring initial velocity in B. If I use Distance formula then answer should be = vsin(x)t+1/8gt^2

Post the complete problem statement. Not everybody has EK books.

 

[knightstale4]

I am studying for EK Osmosis at the moment, and here's my question.

Here's the problem: It is about torque.

There is a 2 kg mass tied to the left end of a 1 m stick, and a 6 kg mass tied to the right end of the meter stick.

Solution: Jordan and Jon pick the left end of the stick or 2 kg mass as their lever arm.

Now here's my question: How do you find the direction of torque?

Jordan and Jon say that to find the direction of the torque, imagine that the rotation point on the left end of the stick is held motionless while we push the stick upwards--the stick would rotate counterclockwise, so torque is counterclockwise?

Confusion: Why would it rotate counterclockwise? I would think the the heavier block would pull it in its direction, and make it go clockwise.

Help, I am scared !

 

[BrokenGlass]

I am studying for EK Osmosis at the moment, and here's my question.

Here's the problem: It is about torque.

There is a 2 kg mass tied to the left end of a 1 m stick, and a 6 kg mass tied to the right end of the meter stick.

Solution: Jordan and Jon pick the left end of the stick or 2 kg mass as their lever arm.

Now here's my question: How do you find the direction of torque?

Jordan and Jon say that to find the direction of the torque, imagine that the rotation point on the left end of the stick is held motionless while we push the stick upwards--the stick would rotate counterclockwise, so torque is counterclockwise?

Confusion: Why would it rotate counterclockwise? I would think the the heavier block would pull it in its direction, and make it go clockwise.

Help, I am scared !

They pick the left end of the stick as the rotation point, not as lever arm.

What they mean is IF the only force acting were a force due to the person pushing the stick upward, the torque would be
counterclockwise.

The NET torque is zero, so the stick would not rotate.

BTW, there is a much easier way to do this problem. Since the ratio of weights is 6/2 = 3, the ratio of distances also has to
be 3, or 75cm/25cm (it's a meter stick). So the stick needs to be supported 75 cm away from the 2kg mass.

HTH

 

[QofQuimica]

Time to close this thread up and start a new one. Please visit the Physics Question Thread 2 to ask your physics questions.