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Finding speed with a pulley?

  • #1
Finding speed with a pulley???

Homework Statement



Two objects are connected by a light string
passing over a light frictionless pulley as
shown in the figure. The 5.9 kg object is
released from rest at a point 4.53 m above the
floor.
The acceleration of gravity is 9.8 m/s2 .

What is the speed of the each object at
the instant before the 5.9 kg hits the floor?
Answer in units of m/s.

Homework Equations





The Attempt at a Solution


I use the energy equation where
PE(initial)=KE(final)
and solve for v but it does not seem to work
 

Answers and Replies

  • #2
181
0


decrease in PE = increase in KE
 
  • #3
tiny-tim
Science Advisor
Homework Helper
25,832
249
Welcome to PF!

Hi physics10189! Welcome to PF! :wink:
I use the energy equation where
PE(initial)=KE(final)
and solve for v but it does not seem to work
Show us your full calculations, and then we can see what went wrong, and we'll know how to help! :smile:
 
  • #4


well here is what i did

mgh=.5mv^2
h=Lcos(theta)
mass cancel out
so this is what i came up with
v=2gLcos(theta)
where L=10m of the string's length
 
  • #5


whoops wrong problem
scrath the last reply

ok its the same way kinda
so here is what i did

PE(initial)=KE(final)
mgh=.5mv^2

masses cancel out
h=4.53m
there for
v=sqrt(2gh)
 
  • #6
181
0


Is the "final" PE of the system zero?
See my earlier post.
 
  • #7


yes because just before the blocks hit the ground can we assume that the height is zero therefore the PE final is zero???
 
  • #8
11
0


What answer are you getting?
 
  • #9
PhanthomJay
Science Advisor
Homework Helper
Gold Member
7,136
476


A figure, or description, showing what is theta, the mass of the other object, etc., sure would help.
 

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