Math Problem Statement

על גלגלת בעלת מסה m ורדיוס R מופעל כוח משיקי קבוע F0. אם הגלגלת מתחילה במנוחה ומסתובבת סביב ציר העובר במרכזה, מהי המהירות הזוויתית שלה בכל זמן?

Solution

The problem involves a rolling disk with mass mm and radius RR, subject to a constant force F0F_0 applied tangentially at its edge. The disk begins at rest, and we are asked to determine the angular velocity of the disk over time.


Steps to Solve:

  1. Newton's Second Law for Rotation: The torque τ\tau about the center of mass of the disk due to the applied force is: τ=F0R\tau = F_0 \cdot R where RR is the radius of the disk.

    According to Newton's second law for rotation: τ=Iα\tau = I \cdot \alpha where II is the moment of inertia of the disk, and α\alpha is the angular acceleration.

    For a solid disk, the moment of inertia about its center is: I=12mR2I = \frac{1}{2} m R^2

    Substituting τ\tau and II: F0R=12mR2αF_0 \cdot R = \frac{1}{2} m R^2 \cdot \alpha

    Solving for α\alpha: α=2F0mR\alpha = \frac{2 F_0}{m R}

  2. Relating Angular Velocity to Angular Acceleration: The angular velocity ω\omega of the disk is related to angular acceleration α\alpha through time tt: ω=αt\omega = \alpha \cdot t

    Substituting α\alpha: ω=2F0mRt\omega = \frac{2 F_0}{m R} \cdot t

    Therefore, the angular velocity of the disk as a function of time is: ω(t)=2F0mRt\omega(t) = \frac{2 F_0}{m R} \cdot t


Final Answer:

The angular velocity of the disk at any time tt is: ω(t)=2F0mRt\omega(t) = \frac{2 F_0}{m R} \cdot t

Let me know if you would like further clarifications or have additional questions! 😊


5 Related Questions:

  1. What is the linear acceleration of the center of mass of the disk?
  2. How would the result change if the disk were a hollow cylinder instead of a solid disk?
  3. What is the relationship between the linear velocity of the disk's center and its angular velocity?
  4. How does the friction force at the contact point of the disk affect its motion?
  5. If the force F0F_0 were applied at the center of the disk, how would the motion differ?

Tip:

Always ensure you know the shape of the object (solid or hollow) to use the correct moment of inertia in rotational motion problems!

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Math Problem Analysis

Mathematical Concepts

Rotational Motion
Torque
Moment of Inertia
Angular Velocity
Newton's Laws for Rotation

Formulas

τ = F × r
τ = I × α
I (solid disk) = (1/2) × m × R^2
ω = α × t

Theorems

Newton's Second Law for Rotational Motion

Suitable Grade Level

Grades 11-12 (Advanced Physics)