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## Homework Statement

two blocks of masses 8kg and 4kg respectively are connected by a string as shown in firgure. calculate their accelerations if they are initially at rest on the floor. after a force of 100N is applied on the pulley in the upward direction (g=10 m/s).

## Homework Equations

Σf=ma

## The Attempt at a Solution

okay, i am used to find the acceleration for the two blocks incase the pulley is fixed (same acceleration for both masses). and i know how to find acceleration for two masses, one is hanged from fixed pulley and the other from moving pulley (a fixed = 2 a moveing). but it's my first time with this type of problem, the fixed pulley itself it moving.

now logically, the whole system will have acceleration, and i think i can find the whole acceleration for the system by considering both masses as one object being lifted (ignoring the mass of the pulley) with a force of 100N.

but How to find each block's acceleraion that's what i don't know. and i found an answer for this question which makes sense but still wasn't enough. it says:

"

__force applied on the pulley will be 100 N__

since pulley is ideal so we can say tension in the string must be 50 N

now we will have

for 4 kg block

plug in all values

weight of other block of mass 8kg is 80 N

its weight is more than the tension in the string so this block will remain at rest and its acceleration must be ZERO"

since pulley is ideal so we can say tension in the string must be 50 N

now we will have

for 4 kg block

plug in all values

weight of other block of mass 8kg is 80 N

its weight is more than the tension in the string so this block will remain at rest and its acceleration must be ZERO"

when i imagine it, i also end up saying block 8kg will have a=0. but i need to reach that by equations.

by the way, i think this system is similar to the atwood's machine which i didn't understand clearly :/ (see attachment )