Simple fixed axis rotational problem

In summary, the conversation discusses finding the magnitude of the force exerted on a uniform stick by a frictionless pivot after it is released. The angular acceleration is calculated to be 11.3 rad/s^2, and the direction to proceed in is suggested. Gravity produces a torque of 13.368 Nm, which can be used to calculate the net torque and determine the force by considering the moment of inertia and the axis of rotation. Ultimately, the correct force of 5.14 N is determined by dividing the net torque by the length of the stick.
  • #1
emtilt
12
0
Homework Statement
A uniform stick of mass M = 2.1 kg and length L = 1.3 m is pivoted at one end. It is held horizontally and released. Assume the pivot is frictionless. Find the magnitude in Newtons of the force Fo exerted on the stick by the pivot immediately after it is released.

I calculated the angular acceleration immediately after the stick's release to be 11.3 rad/s^2 for another step of the problem (and that was the correct solution for that part of the problem), but other than that I don't really know where to begin this problem. Could someone just provide a hint as to the direction I should be going in?
 

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  • #2
Running this through my head..., keeping in mind you have alpha, I would next think about what is causing that alpha.
 
  • #3
Not entirely sure what you mean.

Gravity acts on the mass producing a torque of 13.368 Nm (from [tex]\alpha \frac{1}{3}ML^2 = \tau[/tex])...but I don't know where to go with that...
 
  • #4
You specify a moment of inertia, this depends upon where the axis of rotation is taken. This can be used to calculate the net torque, again with a specific axis of rotation in mind.
 
  • #5
Ah, thanks. I got 5.14, which was correct, by taking the net torque with an axis at the center of the stick. This allowed me to get the torque provided by the pivot by dividing the 13.368 Nm from my previous post by two. The result could then be divided by L=1.3 to get the force.

Thanks again for your help.
 
  • #6
nice job !
 

1. What is a simple fixed axis rotational problem?

A simple fixed axis rotational problem is a type of physics problem that involves an object rotating around a fixed axis. This axis is typically perpendicular to the plane of rotation and passes through the center of mass of the object. Examples of this type of problem include a spinning top, a rotating wheel, or a swinging pendulum.

2. What are the key concepts involved in solving a simple fixed axis rotational problem?

The key concepts involved in solving a simple fixed axis rotational problem include understanding the rotational motion of the object, applying Newton's laws of motion, and using the concepts of angular velocity, angular acceleration, and torque. It is also important to consider the moment of inertia, which is a measure of an object's resistance to rotational motion.

3. How do you determine the direction of rotation in a simple fixed axis rotational problem?

The direction of rotation in a simple fixed axis rotational problem can be determined by using the right-hand rule. This rule states that if you point your right thumb in the direction of the axis of rotation, your fingers will curl in the direction of the object's rotation.

4. What are the units for angular velocity and angular acceleration in a simple fixed axis rotational problem?

The units for angular velocity are radians per second (rad/s), while the units for angular acceleration are radians per second squared (rad/s^2). These units are based on the SI unit for angle, the radian, which is defined as the angle subtended at the center of a circle by an arc equal in length to the radius of the circle.

5. How does the moment of inertia affect the rotational motion in a simple fixed axis rotational problem?

The moment of inertia plays a crucial role in determining the rotational motion of an object in a simple fixed axis rotational problem. The greater the moment of inertia, the more difficult it is to change an object's rotational motion. This means that objects with larger moments of inertia will require more torque to produce the same angular acceleration as objects with smaller moments of inertia.

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