What force must the man pull on the rope to rise with a constant velocity

[suspenc3]

Ok, I already posted this a few days ago but I am bringing it back because i don't quite understand

a man sits in a bosuns chair that dangles from a massless rope, which runs over a massless frictionless pulley, and back down to the mans hand. The combined mass of the man and the chair is 95Kg. with what force must the man pull on the rope to rise with a constant velocity

so..
T=-mg/2

T = 465.5N
this doesn't make sense because if he is to rise any amount, he would have to exert more force that gravity does..Wouldnt he?

 

[quantumdude]

Wouldnt he?

No, the problem says that he is to move at constant velocity. That means that the net force that is applied to him must equal the total weight of the man and the chair exactly.

 

[suspenc3]

Ok..confused now..does this mean that he must exert a force of 931N
Or was my original answer right?

 

[quantumdude]

No, you were right at the beginning. The net force acting on the man + chair is 2T. The man only has to exert a force of T. The problem is supposed to show you the mechanical advantage of using a pulley.

 

[suspenc3]

Ok, Thanks

So part B asks with what magnitude must the man pull on the rope if he is to rise with an upward acceleration of 1.3m/s^2
Any hints?

 

[quantumdude]

Use Newton's second law.

 

[suspenc3]

Now it says that the rope is extended to the ground where a co-worker is pulling on the rope
With what force magnitude must the co-worker pull on the rope to maintain a constant velocity?

now would the answer be 931N

 

[quantumdude]

Yesiree. That's because the force applied to the chair + man is only T, whereas before it was 2T.

 

[suspenc3]

Now it is asking for the magnitude of the forces on the ceiling from the pulley systems

Would this part just be the weight of the man+chair +the force applied?