Math Problem Statement

During a very quick stop, a car decelerates at 7.20 m/s2. What is the angular acceleration (in rad/s2) of its 0.300 m radius tires, assuming they do not slip on the pavement? (Indicate the direction with the sign of your answer. Assume the tires initially rotated in the positive direction.) Find the following: The number of revolutions the tires make before stopping when their initial angular velocity is 97 rad/s; how many seconds it takes for the car to come to a complete stop; the distance the car travels (in m)

Solution

To solve this problem, we will break it into parts and use the relationships between linear and angular motion:

1. Angular Acceleration (α):

We are given:

  • Linear deceleration (ata_t) = 7.20m/s27.20 \, \text{m/s}^2
  • Radius of the tires (rr) = 0.300m0.300 \, \text{m}

The angular acceleration (α\alpha) is related to the linear acceleration by: α=atr\alpha = \frac{a_t}{r} Substitute the values: α=7.200.300=24.0rad/s2\alpha = \frac{7.20}{0.300} = 24.0 \, \text{rad/s}^2

Since the deceleration is in the opposite direction of the initial rotation, the angular acceleration will have a negative sign: α=24.0rad/s2\alpha = -24.0 \, \text{rad/s}^2


2. Number of Revolutions (θ in revolutions):

The relationship between angular displacement (θ\theta), initial angular velocity (ω0\omega_0), angular acceleration (α\alpha), and time (tt) is: θ=ω0t+12αt2\theta = \omega_0 t + \frac{1}{2} \alpha t^2

But first, we need to find the time it takes to stop.


3. Time to Stop (t):

The angular velocity decreases uniformly until it reaches zero. The time to stop is given by: t=ω0αt = \frac{\omega_0}{|\alpha|} Substitute the values: t=9724.0=4.04secondst = \frac{97}{24.0} = 4.04 \, \text{seconds}


4. Angular Displacement (θ\theta):

The total angular displacement can be calculated using the equation: θ=ω0t+12αt2\theta = \omega_0 t + \frac{1}{2} \alpha t^2 Substitute the known values (ω0=97rad/s\omega_0 = 97 \, \text{rad/s}, t=4.04st = 4.04 \, \text{s}, and α=24.0rad/s2\alpha = -24.0 \, \text{rad/s}^2): θ=(97)(4.04)+12(24.0)(4.04)2\theta = (97)(4.04) + \frac{1}{2}(-24.0)(4.04)^2 First term: 97×4.04=391.8897 \times 4.04 = 391.88 Second term: 12(24.0)(4.04)2=195.84\frac{1}{2}(-24.0)(4.04)^2 = -195.84 θ=391.88195.84=196.04radians\theta = 391.88 - 195.84 = 196.04 \, \text{radians}

Convert to revolutions: Revolutions=θ2π=196.042π31.2revolutions\text{Revolutions} = \frac{\theta}{2\pi} = \frac{196.04}{2\pi} \approx 31.2 \, \text{revolutions}


5. Distance Traveled (d):

The distance traveled by the car is related to the angular displacement by: d=rθd = r \theta Substitute the values (r=0.300mr = 0.300 \, \text{m}, θ=196.04rad\theta = 196.04 \, \text{rad}): d=(0.300)(196.04)58.81md = (0.300)(196.04) \approx 58.81 \, \text{m}


Final Results:

  1. Angular acceleration: 24.0rad/s2-24.0 \, \text{rad/s}^2
  2. Time to stop: 4.04seconds4.04 \, \text{seconds}
  3. Number of revolutions: 31.2revolutions31.2 \, \text{revolutions}
  4. Distance traveled: 58.81m58.81 \, \text{m}

Let me know if you would like details on any of the steps or have further questions. Here are 5 questions related to this problem for you:

  1. How is angular acceleration connected to linear acceleration in general?
  2. Why is the angular displacement in radians converted to revolutions?
  3. How would the problem change if the tires slipped on the pavement?
  4. What factors influence the distance traveled during deceleration?
  5. How could this problem be solved graphically instead of mathematically?

Tip: Always pay attention to unit consistency, especially when converting between radians and revolutions.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Linear and angular motion
Kinematics equations
Relationship between linear and angular variables

Formulas

α = at / r
t = ω₀ / |α|
θ = ω₀t + (1/2)αt²
d = rθ

Theorems

Kinematic equations for rotational motion
Relationship between linear and angular quantities (a = rα)

Suitable Grade Level

Grades 11-12