Pulley HELP

  • Thread starter SUXinPHY
  • Start date
  • #1
26
0

Homework Statement


a box weighing 77N rest on a table. a rope tied to the box runs vertically upward over a pulley and a weight is hung from the other end. determine the force that the table everts on the box if the weight hanging on the other side of the pulley weighs 30N.

(box in on the left n weight on the right hand side of the pulley)


Homework Equations


box
F=mg-T
ma=mg-T
weight
F=T-mg
ma=T-mg

The Attempt at a Solution


i let

T of box= T of weight
mg-ma=ma-mg
2ma=30N + 77N
ma=107N / 2
F=53.5N

(i think i am missing something in the equation)
 

Answers and Replies

  • #2
361
21
If the weight hanging opposite the box was 77N, what force would the table exert?
 
  • #3
26
0
i am not sure but i will be guessing its a normal force.....
 
  • #4
361
21
The table only exerts a force equal to what is not supported by tension in the rope.

As one of your formulas you have T of box= T of weight. You know that since the system is at rest and the weight is suspended the tension has to be equal to the weight. The tension in the rope is pulling up on the box with a force equal to the weight. The table supports the difference between the weight of the box and the weight of the weight.
 
  • #5
26
0
alright i think i get wat u mean..... if i go wrong i will let u know
 

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