Math Problem Statement

A heavy flywheel is accelerated (rotationally) by a motor that provides constant torque and therefore a constant angular acceleration α. The flywheel is assumed to be at rest at time t = 0 in Parts A and B of this problem. Assume that the motor has accelerated the wheel up to an angular velocity ω1 with angular acceleration α in time t1 . At this point, the motor is turned off and a brake is applied that decelerates the wheel with a constant angular acceleration of −5α . Find t2 , the time it will take the wheel to stop after the brake is applied (that is, the time for the wheel to reach zero angular velocity).

Solution

To find the time t2t_2 it will take for the wheel to stop after the brake is applied, we can use the following kinematic equation for rotational motion:

ωf=ωi+αt\omega_f = \omega_i + \alpha t

where:

  • ωf\omega_f is the final angular velocity (which will be zero since the wheel is stopping),
  • ωi=ω1\omega_i = \omega_1 is the initial angular velocity at the moment the brake is applied,
  • α=5α\alpha = -5\alpha is the constant angular deceleration applied by the brake, and
  • t=t2t = t_2 is the time we need to find.

Since we know that the wheel's angular velocity will eventually reach zero, we can set up the equation as:

0=ω1+(5α)t20 = \omega_1 + (-5\alpha)t_2

Rearranging this equation to solve for t2t_2, we get:

t2=ω15αt_2 = \frac{\omega_1}{5\alpha}

Thus, the time t2t_2 it will take the wheel to stop after the brake is applied is:

t2=ω15αt_2 = \frac{\omega_1}{5\alpha}

This time depends on the initial angular velocity ω1\omega_1 and the deceleration 5α-5\alpha.

Would you like further details on how to apply this formula in specific cases or explanations of the variables?

Here are five related questions to explore the concept further:

  1. How would t2t_2 change if the deceleration were doubled to 10α-10\alpha?
  2. What would be the effect on t2t_2 if ω1\omega_1 were halved?
  3. How would you calculate the angular displacement of the wheel during deceleration?
  4. How does constant torque influence the angular acceleration in rotational motion?
  5. If the flywheel started with an initial angular velocity, how would the approach change?

Tip: When solving problems involving constant acceleration or deceleration, kinematic equations for linear motion have direct analogs in rotational motion, where linear quantities (like velocity and acceleration) are replaced by angular quantities.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Rotational Motion
Kinematics
Angular Velocity
Angular Acceleration

Formulas

ω_f = ω_i + α t
t_2 = ω_1 / (5α)

Theorems

Kinematic equation for rotational motion

Suitable Grade Level

Grades 10-12