# Any Help is appriciated: 3 - Kinematic Problems

1. Apr 5, 2005

### naren11

Hello,

Sorry about this and please don't think I m a lazy guy who is posting an assinment that is due tomorrow. I m scanning it and posting this because these questions do not involve numbers but require reasoning in which i m bad at. I m currenly taking a Physics 2nd year distance ed course so i dont really have friends to help me with these questions. So considering u guys as my friends I post the last 3 questions from my problem set.

1st & 2nd Question:

http://img125.exs.cx/img125/4971/lastscan1bv.jpg

3rd Question

http://img201.exs.cx/img201/4290/lastscan27cv.jpg

Plz answer much as possible. I m preparing for my finals and these questions are recommended for me through my tutor. Thank you very much! I will ck the forums couple of hours later

Last edited: Apr 5, 2005
2. Apr 6, 2005

### asrodan

From the diagram [1] $$ma = mg - T$$

$$\tau = RT = I\alpha$$

$$\alpha = \frac{RT}{I}$$

We also know that [2] $$\alpha = \frac{a}{R}$$ so

[3] $$a = \frac{R^2T}{I}$$

from [1] $$a = g - \frac{T}{m}$$

substitute [3] $$\frac{R^2T}{I} = g - \frac{T}{m}$$

$$T = \frac{g}{\frac{R^2}{I}+\frac{1}{m}}$$ = $$\frac{Img}{mR^2+I}$$ [4]

Divide the top and bottom of [4] by I to get the equation for 13 (c)

Substitute [4] into [3] $$a = \frac{R^2mg}{mR^2+I}$$

divide this by $$R^2m$$ to get the

equation for 13 (b)

Substitute (b) into [2] to get the equation for 13 (a)

For question 14, You just need to use conservation of energy and rearrange for v.

For question 15, all you need to know is that

$$\alpha = \frac{\tau}{I}$$ and the expressions for I for the rod and masses.

Last edited: Apr 6, 2005