Physics Final: Rotation Questions - Get Help Now!

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In summary: If you could make it so that the ladder never slips, then the torque and force would be zero. But if you can't make it so that the ladder never slips, then you would have to find a way to make the other forces zero as well.
  • #1
harsh
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Hey everyone, I am making this thread to find out about concepts.
So I have a physics final tommorow, and I have friends who told me that there is a lot of rotation on it. Now, I think i know rotation well, but if any of you have good problems that you want to give me, or any suggestions or anything like that, I would really appreciate it.

Btw..I just joined yesterday. Thanks in advance.
 
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  • #2
okay i try to find

It seems to me u are of Indian Origin
 
  • #3
Well, IMO, doing work with rotating bodies is just like using Newton's laws, but replacing linear quantities with angular ones:

[tex]\begin{align*}
v = d / t &\rightarrow \omega = \theta / t\\
F = m a &\rightarrow \tau = I \alpha
\end{align*}[/tex]

and so on.

- Warren
 
  • #4
u try this

A sphere of radius R is projected with a reverse spin [tex]\omega_0[/tex] down a rough inclined plane with a speed [tex]v_0[/tex] for which coefficient of friction is [tex]\mu > \tan\theta where \theta[/tex] is angle of incline. Find min [tex]\omega[/tex] so that it turns back.
 
  • #5
Ok -- here's a fun one:

A ladder is at rest, touching the floor and the wall at an angle θ with the horizontal. Assuming that the ladder has a uniform distribution of mass, and that there is no friction, at what angle does the top of the ladder leave the wall?
 
  • #6
Ok, so I have been thinking about that problem.
I honestly have no idea where to start.

Would you kindly try and give me a bit of a starting point or something to think about...

Thanks for the problem.

Oh, and work and energy problems would be good too.
 
  • #7
Thanks NateTG, this seems like a statics problem

problem..Let me try and work it out
 
  • #8
[tex]\mu > \tan\theta [/tex] implies

f>=mg sin(theta)
Hence the sphere will turn back if at the moment its Centre of mass comes to stop it must have angular speed in same dir as [tex]\omega_0[/tex]
 
  • #9
Ok, this is what I have so far for the problem give to me by NateG.

Since there is no friction between the wall and the ladder. So there are 4 forces:

Ff in the horizontal at the floor
N1 vertical at the floor
N2 horizontal at the top of the ladder (wall)
mg: the weight at the center of the ladder

So sum of the forces and torques must equal zero

F - N2 = 0

N1- mg = 0

Torques:
-mg(L/2) + (N1cos(q)L)

is there a torque due to the frictional force?
 
  • #10
No, I aparently didn't make it clear enough. The ladder starts slipping, and you want to find when the motion of the ladder is such that the top of the ladder leaves the wall. The net torque and net force should both be non-zero.

IIRC the problem is pretty harsh.
 

FAQ: Physics Final: Rotation Questions - Get Help Now!

What topics should I focus on for the rotation section of the physics final?

For the rotation section of the physics final, you should focus on understanding concepts such as angular velocity, angular acceleration, moments of inertia, torque, and rotational kinetic energy. It is also important to understand the relationships between these concepts and how they relate to linear motion.

How can I prepare for the mathematical calculations in the rotation section of the physics final?

To prepare for the mathematical calculations in the rotation section, it is important to practice solving problems involving rotational motion. This includes using equations such as the rotational kinematics equations, the rotational dynamics equations, and the moment of inertia equation. It may also be helpful to review trigonometric functions, as they are often used in rotational motion calculations.

What are some common mistakes to avoid in the rotation section of the physics final?

Some common mistakes to avoid in the rotation section of the physics final include forgetting to convert units, using incorrect signs or directions in calculations, and not considering the effects of external forces on rotational motion. It is also important to double check your calculations and make sure they make physical sense.

How can I visualize rotational motion to better understand it for the physics final?

To visualize rotational motion, it can be helpful to use diagrams or animations to represent the motion of an object. You can also use everyday objects, such as a spinning top or a bicycle wheel, to see how they rotate and understand the concepts of angular velocity and acceleration. Additionally, using the right-hand rule can help you understand the direction of rotation in a given scenario.

Are there any real-world applications of the concepts covered in the rotation section of the physics final?

Yes, there are many real-world applications of rotational motion. For example, understanding rotational motion is important in designing and analyzing the performance of machines, such as motors and engines. It is also essential in fields such as sports, where rotational motion is involved in activities like throwing a ball or swinging a golf club. Additionally, the principles of rotational motion are used in astronomy to study the motion of celestial bodies.

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