How can I solve these physics problems involving torque and rotational energy?

In summary, the quizes are the last chance for a B in this class, and the person has attached a copy of the problems with the solutions. The quizes are open book, and the person is hoping somebody can review the work.
  • #1
Max CR
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0
In Physics I have a C average right now. These two quizes are my last chance at bringing my grade up to a B for this class. I have attached a copy of all of the problems that are on these two quizes totalling seven questions. THis is open book take home quiz where we can work with whoever we want.

I was hoping that somebody here can look over my work and tell me if I made any mistakes. I have made the attempt, now I am hoping someone could review it.

Thanks. Enclosed are the quizes and the work I have done on them

http://i289.photobucket.com/albums/ll229/Cleaver97/th_Quiz2001.jpg

http://i289.photobucket.com/albums/ll229/Cleaver97/th_Quiz1001.jpg
 
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  • #2
2nd paper Q5: The amount of rotational KE an object has depends on the object's moment of inertia, hence that cannot be an answer. (Hint: Think conservation of energy, what is always the same of two objects of the same mass going down the same height?)

Otherwise, well done!
 
  • #3
I would havve to say angular speed?
 
  • #4
No, you see, angular speed is related to the rotational kinetic energy of the object, which are not equal. Now, examine what is similar for these two objects, there's mass and there's the starting height. These two describe a certain physical quantity, what is it?
 
  • #5
Aha! It is momentum correct? It is the only one.
 
  • #6
Again, no. Conservation of energy states that initial energy = final energy. What form is the initial energy in? What are the final states of energy? Are the total energy for the two objects similar?
 
  • #7
I understand now. They both are rolling down an incline with the force of gravity. Therefore it is gravitational PE? I believe it is. THanks for the help. I really appreciate it.
 
  • #8
That's it. Because initially, both the mass and the heights are the same, the GPE has to be equal. By conservation of energy, GPE = rot. KE + translational KE.

Since I is different, rot KE. has to be different (and by extension angular speed), and since the total energy for the two is equal, if rot KE differs, trans. KE also differs (and by extension, momentum also differs).
 
  • #9
Ohh .. I understand now. THanks a loot!
 

1. How do I calculate torque?

To calculate torque, you need to know the force applied and the distance from the pivot point. The formula for torque is: torque = force x distance. Make sure to use the correct units for force (newtons) and distance (meters).

2. What is the difference between clockwise and counterclockwise torque?

Clockwise torque is when the force applied causes an object to rotate in a clockwise direction, while counterclockwise torque is when the force applied causes an object to rotate in a counterclockwise direction. This is important to know when determining the net torque on an object.

3. How do I calculate the net torque on an object?

The net torque on an object is the sum of all the individual torques acting on the object. This can be calculated by adding up all the clockwise torques and subtracting all the counterclockwise torques. The net torque is important in determining the rotational motion of an object.

4. How do I solve a rotational energy problem?

To solve a rotational energy problem, you need to know the moment of inertia of the object (which depends on its shape and mass distribution) and the angular velocity of the object. The formula for rotational energy is: rotational energy = 1/2 x moment of inertia x (angular velocity)^2. Make sure to use the correct units for moment of inertia (kg*m^2) and angular velocity (rad/s).

5. What is the relationship between torque and rotational energy?

Torque and rotational energy are closely related. Torque is the force that causes an object to rotate, while rotational energy is the energy associated with an object's rotation. They are related by the formula: torque = rate of change of rotational energy. This means that the net torque acting on an object is equal to the change in its rotational energy over time.

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