Verification: Hanging mass on cylinder. Moment of inertia

pat666

1. The problem statement, all variables and given/known data
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))

2. Relevant equations

solved but unsure

3. 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. ive 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

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

kuruman

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.