# Welded discs dropped whilst string wrapped around one, find downward a

1. Mar 31, 2013

### Fluxthroughme

Image included to show I've made an attempt, but my attempt left me realising I just don't know where to go. If someone could point me in the right direction, it'd help a lot.

2. Mar 31, 2013

### rcgldr

You don't need to do energy calculations for this problem. One of the unknowns is the downwards acceleration of the block, and this affects the downwards force that the block exerts onto the string.

What is the equation for the force the block exerts on the string if the block is accelerating downwards at a, where a is the rate of acceleration of the block?

Last edited: Mar 31, 2013
3. Mar 31, 2013

### Fluxthroughme

Ok, I got the correct answer this time, by using $1.5g - T = 1.5a$, $a=r\alpha$, and $\tau = rF$ :) Thank you!