Verification: Hanging mass on cylinder. Moment of inertia

[pat666]

Homework Statement

A 15.0 kg bucket of water is suspended by a very light rope wrapped around a solid cylinder 0.300 m in diameter with a mass of 12.0 kg. The cylinder pivots on a frictionless axle through its centre. The bucket is released from rest at the top of a well and falls 10.0 m to the water.
a) What is the tension in the rope while the bucket is falling? my answer: 42.15N
b) With what speed does the bucket strike the water? my answer: 11.8m/s
c) What is the time of the fall? my answer: 1.69s
d) While the bucket is falling, what is the force exerted on the cylinder by the axle: my answer: 159.87N this is the one that i am really unsure of (and a))

Homework Equations

solved but unsure

The Attempt at a Solution

could someone who knows what there doing please check my answers, i wouldn't ask if it wasn't important.. thanks in advance.

 

[ehild]

It looks good. How did you get the force of the axle?

ehild

 

[pat666]

actually that part was wrong, it is actually just F=ma and it turns out to be 105N i hope. I've actually been getting a lot of help from someone else on PF

 

[pat666]

Hi, just a quick question. why do they give the radius of the cylinder if it is not needed, is there a way to solve these problems that does require the radius?
I have another very similar problem to this that i didnt use the radius for either

 

[Squeezebox]

Hi, just a quick question. why do they give the radius of the cylinder if it is not needed, is there a way to solve these problems that does require the radius?
I have another very similar problem to this that i didnt use the radius for either

They could be giving you extra info for you to sift through and see what's relevant and what's not.

 

[kuruman]

Hi, just a quick question. why do they give the radius of the cylinder if it is not needed, is there a way to solve these problems that does require the radius?
I have another very similar problem to this that i didnt use the radius for either

If the problem gave you a pulley with a moment of inertia that cannot be calculated from a formula, then you do need the radius. However, the method is the same.