2 mp problems that I sorta understnad but dont?

  • Thread starter Thread starter RhysticGenesis
  • Start date Start date
Click For Summary
SUMMARY

The discussion centers on solving two problems related to angular motion and kinematics. The first problem involved correcting an equation for angular displacement, where the user initially missed adding +π/2. The second problem required calculating the time for an electric fan to come to rest, given an angular acceleration of -1.57 rev/s². The user initially calculated the time as 1.70 seconds but later arrived at an incorrect value of 173.252 seconds, prompting further clarification on unit consistency and equation application.

PREREQUISITES
  • Understanding of angular motion equations, specifically \(\theta(t)\) and \(\omega(t)\)
  • Familiarity with angular velocity units, particularly revolutions per minute (rev/min)
  • Knowledge of angular acceleration and its impact on motion
  • Ability to apply trigonometric functions in physics equations
NEXT STEPS
  • Review the application of angular motion equations, focusing on \(\theta(t) = \theta(0) + \omega_{0}t + \frac{1}{2}\alpha t^{2}\)
  • Learn about unit conversions between rev/min and rev/s for angular velocity
  • Study the concept of angular acceleration and its calculation in uniform motion scenarios
  • Practice solving problems involving trigonometric corrections in physics equations
USEFUL FOR

Students studying physics, particularly those focusing on rotational dynamics and kinematics, as well as educators looking for problem-solving strategies in angular motion.

RhysticGenesis
Messages
10
Reaction score
0
2 mp problems that I sort of understnad but dont??

Edit: I figured out first problem... I was missing + pi/2 in the equation but still a little screwed up on second problem :

Edit: Figured both of em out with help. thanks for the help
 
Last edited:
Physics news on Phys.org
RhysticGenesis said:
I came up with :
R*sin(omega*t)*x_unit+R*cos(omega*t)*y_unit

and it told me it was wrong and to check over my signs?? :confused:
Check your answer for \omega t = 90 degrees and see if your signs are correct. Note: Positive \omega means it rotates counter-clockwise!
 
Last edited:
Yeah I just got it before I read your post guess I was little stupid on that one heh.. but second one I still don't get what I am doing wrong?
 
\theta (t)=\theta(0)+\omega_{0}t+\frac{1}{2}\alpha t^{2}
\omega (t)=\omega(0)+\alpha t

That's all u have to use...Properly.Pay attention to signs & initial conditions...

Daniel.
 
dont need help anymore heh got both answerss I needed I feel quite stupid now actually heh
 
RhysticGenesis said:
The other problem is An electric fan is turned off, and its angular velocity decreases uniformly from 540rev/min to 200rev/min in a time interval of length 3.60s. How many more seconds are required for the fan to come to rest if the angular acceleration remains constant at the value calculated in Part A? The value calculated in part a was the angular acceleration which was -1.57 rev/s^2
OK.
I came up with answer 1.70 seconds by equating inital velocity (540 rev/min) plus the acceleration (-1.57 rev/s^2) times time (3.6 seconds) and set it all equal to zero and got 1.7 but I just did it over and I came out with 173.252?? help?
Not clear what you did. Use \omega_f = \omega_i + \alpha t; be sure to use proper units for \omega.
 
Last edited:

Similar threads

  • · Replies 29 ·
Replies
29
Views
1K
Replies
8
Views
2K
  • · Replies 5 ·
Replies
5
Views
786
  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 17 ·
Replies
17
Views
1K
  • · Replies 19 ·
Replies
19
Views
1K
  • · Replies 3 ·
Replies
3
Views
829
  • · Replies 3 ·
Replies
3
Views
890
  • · Replies 21 ·
Replies
21
Views
2K
  • · Replies 6 ·
Replies
6
Views
1K