2 mp problems that I sorta understnad but dont?

[RhysticGenesis]

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

 

[Doc Al]

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??

Check your answer for \omega t = 90 degrees and see if your signs are correct. Note: Positive \omega means it rotates counter-clockwise!

 

[RhysticGenesis]

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?

 

[dextercioby]

\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.

 

[RhysticGenesis]

dont need help anymore heh got both answerss I needed I feel quite stupid now actually heh

 

[Doc Al]

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.