What is the Angular Speed of the Spool After the Bucket Falls?

AI Thread Summary
The discussion focuses on using conservation of energy to calculate the angular speed of a spool after a bucket falls. Initially, the user incorrectly included the mass of the spool in the kinetic energy equations, leading to an incorrect answer. Upon realizing the mistake, they corrected the calculations by using only the mass of the bucket for kinetic energy terms. The revised calculations yielded a velocity of 6.753 m/s and an angular speed of 14.06 rad/s. The importance of correctly identifying mass in energy equations is emphasized.
Touchme
Messages
41
Reaction score
0
Use conservation of energy to determine the angular speed of the spool shown in Figure P8.36 after the 3.00 kg bucket has fallen 4.65 m, starting from rest. The light string attached to the bucket is wrapped around the spool and does not slip as it unwinds.

I used conservation of energy.
(KEr + KEt + mgh)i = (KEr + KEt + mgh)f
0 + 0 + (3 x 9.8 x 4.65) = [.5(.5Mr^2)w^2] + .5(Mv^2) + 0
136.71 = (.25Mr^2)w^2 + .5Mv^2
136.71 = (.25 x 5 x v^2) + (.5 x 5 x v^2)
v = 7.39
w = 12.324

The ans is not correct, what am i doing wrong?

Thank you for lookin but I manage to see my mistake. I used the wrong mass for the KEt
 

Attachments

  • p8-36.gif
    p8-36.gif
    6.7 KB · Views: 569
Last edited:
Physics news on Phys.org
and KEr. The mass for the KEt and KEr should be the mass of the bucket only not the spool and the bucket. 0 + 0 + (3 x 9.8 x 4.65) = [.5(.5Mb^2)w^2] + .5(Mbv^2) + 0136.71 = (.25Mb^2)w^2 + .5Mbv^2136.71 = (.25 x 3 x v^2) + (.5 x 3 x v^2)v = 6.753w = 14.06
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top