Title: Angular acceleration of a frictionless pulley Post by: jgrins on Nov 8, 2014 A frictionless pulley, which can be modeled as a 0.86kg solid cylinder with a 0.31m radius, has a rope going over it, as shown in the figure. (Figure 1 attached)
The tensions in the rope are 12N and 10N . What is the angular acceleration of the pulley? I've attached the drawing I did so far for the problem. I know I need to use either the moment arm or the radial arm but I don't know the angles to find them, so I'm not sure what the next step is. I know I need to find the net torque that is exerted by the pulley, and I can find the moment of inertia by I=1/2MR2. If someone could give me a hint, that would be great, not necessarily to solve. Thanks! Title: Re: Angular acceleration of a frictionless pulley Post by: savio on Nov 8, 2014 Similar Question A frictionless pulley, which can be modeled as a 0.86kg solid cylinder with a 0.37m radius, has a rope going over it, as shown in the figure. The torque is (12 - 10)*0.37 N-m = 0.74 N-m The moment of inertia of a solid cylinder is ½*m*r² = 0.05887 kg-m² The angular acceleration is T/I = 12.57 kg-m² which is the correct answer except that it should have only 2 significant figs; a = 13 kg-m² Title: Re: Angular acceleration of a frictionless pulley Post by: jgrins on Nov 8, 2014 Okay but how did you find torque = (12-10)*.037 N-m?
I know that you subtract the 10N force bc it's clockwise, but where did you get the value .37 N-m? Is it the same as the radius? Sorry, I want to understand as well, not just get an answer. And are you assuming that the 12-10N is the perpendicular force, because it looks like they're at an angle with the figure? Title: Re: Angular acceleration of a frictionless pulley Post by: skip5284 on Nov 8, 2014 Torque = T = (12-10) * 0.3 = 0.6
I = 0.5 m*r2 = 0.03645 So α = T/I α = 16.46 rad/s2 Title: Re: Angular acceleration of a frictionless pulley Post by: bio_man on Nov 8, 2014 Content hidden
Title: Re: Angular acceleration of a frictionless pulley Post by: savio on Nov 9, 2014 Did any of these help you?
Title: Re: Angular acceleration of a frictionless pulley Post by: jgrins on Nov 11, 2014 Yeah they did. I messed up because I assumed there was an angle between the tension and the pulley but my professor told me its just perpendicular to the pulley so torque=rF
Title: Re: Angular acceleration of a frictionless pulley Post by: bio_man on Nov 11, 2014 Awesome, marking it solved :)
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