# mechanics pulley question help

#1
Attached below. I have to draw the forces acting on it before and after the 12kg htis the ground. Before i am confused, would the 5kg mass have tension acting in both directions of the pulley meaning 2 tension forces are acting on it?

And for when the 12kg hits the ground i put for the 12kg the weight and normal force with the ground and no tension. Would this mean the acceleration now acting in the opposite direction so i would just put the friction force acting the other way? Also in this case for the 5kg would the tension be on the right hand side of the pulley or will there still be 2 tension forces acting on the 5kg?
0
5 years ago
#2
(Original post by ErniePicks)
Attached below. I have to draw the forces acting on it before and after the 12kg htis the ground. Before i am confused, would the 5kg mass have tension acting in both directions of the pulley meaning 2 tension forces are acting on it?

And for when the 12kg hits the ground i put for the 12kg the weight and normal force with the ground and no tension. Would this mean the acceleration now acting in the opposite direction so i would just put the friction force acting the other way? Also in this case for the 5kg would the tension be on the right hand side of the pulley or will there still be 2 tension forces acting on the 5kg?
Before the 12kg block hits the ground there is tension in both strings. The tensions in the strings may differ. Once the 12kg block has hit the floor there in no tension in the string but there is still tension in
1
#3
(Original post by Cryptokyo)
Before the 12kg block hits the ground there is tension in both strings. The tensions in the strings may differ. Once the 12kg block has hit the floor there in no tension in the string but there is still tension in
i am not sure how to find t1 and t2 as all the previous questions i have done the tension was the same in the string and just T and not T1 or t2.
0
#4
Like usually i calculate a first but in this case i'm not sure, as i usually write down 2 independent equations for the masses involved and add or subtract them together and the T's cancel out and i find out a. But in this case for the eqn's it's T1 and T2 and they dont cancel out.
0
5 years ago
#5
(Original post by ErniePicks)
Like usually i calculate a first but in this case i'm not sure, as i usually write down 2 independent equations for the masses involved and add or subtract them together and the T's cancel out and i find out a. But in this case for the eqn's it's T1 and T2 and they dont cancel out.
Good to spot that the tensions are different.

You have three blocks, so you can get three equations of motion, one for each block.

And yes for the 5kg block you have tension both sides, and the equation of motion for this block ties together T1 and T2 allowing you to eliminate them.

Regarding the friction after the 12kg block hits the ground. I'd like to see the original question, as I think the answer is going do depend on what precisely is being asked.
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