Angular Displacement: Solving for a Mountain Bike Wheel

In summary, the problem involves a wheel on a mountain bike with a constant angular acceleration starting from rest at t=0s. At t=5.15s, the angular velocity of the wheel is +7.66rad/s. The angular acceleration continues until t=13.6s, after which the angular velocity remains constant. The question asks for the angular displacement of the wheel from t=0s to t=28.0s. This can be calculated by dividing the motion into two parts, with the first part having a constant acceleration of 0.563 rad/s^2 and the second part having a constant velocity of 7.66 rad/s. The total displacement is then found by adding the individual displacements from
  • #1
SnowOwl18
71
0
Alright, this problem is really starting to bug me.

----Starting from rest at t0 = 0s, a wheel on a mountain bike has a constant angular acceleration. When t = 5.15s, the angular velocity of the wheel is +7.66rad/s. The angular acceleration continues until t = 13.6s, after which time the angular velocity remains constant. What is the angular displacement of the wheel in the time interval from t = 0 to 28.0s?----

I divided it into two parts, since angular acceleration is constant from t=0s to t=13.6s, and isn't for the remaining portion. So for that first part, I calculated the angular acceleration by doing change in angular velocity or change in time...7.66rad/s / 13.6s = 0.562 rad/s^2. And then I solved for Theta = 0.5 A T^2 ...and I got 52.088 rad. And then for the second part I found the acceleration over the remaining 14.4s and got an acceleration (through the same process) of 0.532 rad/s^2...and then I solved for Theta of that portion and then added my two numbers to get 107.24 rad. But it's wrong. Any guidance would be much appreciated. Thanks! :)
 
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  • #2
SnowOwl18 said:
I divided it into two parts, since angular acceleration is constant from t=0s to t=13.6s, and isn't for the remaining portion. So for that first part, I calculated the angular acceleration by doing change in angular velocity or change in time...7.66rad/s / 13.6s = 0.562 rad/s^2. And then I solved for Theta = 0.5 A T^2 ...and I got 52.088 rad.
You made a mistake in calculating the acceleration: 7.66 rad/s is the angular speed at t = 5.15 s, not t = 13.6 s. So the change in time is 5.15 s.

And then for the second part I found the acceleration over the remaining 14.4s and got an acceleration (through the same process) of 0.532 rad/s^2...and then I solved for Theta of that portion and then added my two numbers to get 107.24 rad.
For the second part, the acceleration is zero. They tell you that the speed is constant.
 
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  • #3
O ok...so for the first part (t=0s to t=5.15s) 7.66/10.3= 0.738 rad. I had thought the acceleration would be zero because of constant velocity (now if I only followed my intuition!)...so that would mean I just multiply the speed by the time to get distance. So if I multiply 7.66 by the remaining time, 22.85s, and get 175.769 rad...and then add the 0.738 rad i found before...would that be the correct way to find the answer?
 
  • #4
First, let me apologize for telling you to use the average velocity to find the displacement. You can't use that method since you don't have the final speed at the end of the first part of the motion. D'oh! I must have been sleeping. (I removed that advice from the previous post.)
SnowOwl18 said:
O ok...so for the first part (t=0s to t=5.15s) 7.66/10.3= 0.738 rad. I had thought the acceleration would be zero because of constant velocity (now if I only followed my intuition!)...so that would mean I just multiply the speed by the time to get distance. So if I multiply 7.66 by the remaining time, 22.85s, and get 175.769 rad...and then add the 0.738 rad i found before...would that be the correct way to find the answer?
Here's what you do. As you stated earlier, treat the motion in two parts (1) accelerated (from t = 0 to 13.6) and (2) constant speed (from t = 13.6 to 28.0).

For part 1, find the acceleration. (See my previous post.) Then use that acceleration to do two things: find the displacement (using [itex]\theta = 1/2 \alpha t^2[/itex]) over the entire interval, and find the find speed at the end of the interval (using [itex]\omega_f = \alpha t[/itex]).

For part 2, you have the speed and the time so use [itex]\theta = \omega t[/itex].

Now just add the two displacements.
 
  • #5
For part two I did 7.66 rad/s x 14.4s = 110.304 rad

Part one...a= deltav/deltat...7.66rad/s / 13.6s = 0.563 rad/s^2 ...
.5 x 0.563 x 13.6^2 = 52.07 rad

When added together, I get 162.4 rad total...but the program says I'm wrong...and unfortunately, I have only one try left. Sorry to keep bothering you, but do you see another mistake? Thanks so much for your help thus far...I don't know why I keep messing this up. :/
 
  • #6
You are still making errors in both parts.
SnowOwl18 said:
For part two I did 7.66 rad/s x 14.4s = 110.304 rad
7.66 rad/s is only the speed at t=5.15s. It is not the speed you need for the "constant speed" part of the motion (part 2). You have to figure out that speed. See my last post for how to figure out that speed using the acceleration from part 1.
Part one...a= deltav/deltat...7.66rad/s / 13.6s = 0.563 rad/s^2 ...
.5 x 0.563 x 13.6^2 = 52.07 rad
See my first post. You are using the wrong time in calculating the acceleration: [itex]\alpha = \Delta \omega/\Delta t = (7.66)/(5.15) [{rad}/s^2][/itex].
 

What is angular displacement?

Angular displacement is the measure of the change in the angle of an object's position, typically measured in radians or degrees.

How is angular displacement related to mountain bike wheels?

Angular displacement is often used in physics to calculate the rotation of objects, including the rotation of mountain bike wheels. It can help determine the distance traveled and the speed of the bike.

What information is needed to solve for angular displacement of a mountain bike wheel?

To solve for angular displacement of a mountain bike wheel, you will need to know the initial angle of the wheel, the final angle of the wheel, and the radius of the wheel.

Can angular displacement affect the performance of a mountain bike?

Yes, angular displacement can affect the performance of a mountain bike. The more angular displacement there is, the more the wheel will rotate, resulting in a longer distance traveled and potentially higher speeds.

What are some real-world applications of solving for angular displacement in mountain biking?

Solving for angular displacement in mountain biking can help riders understand how their wheels are rotating and how their speed is affected by different angles. It can also be used to make adjustments to the bike's suspension and help improve overall performance.

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