# Finding speed with a pulley?

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.

## 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

decrease in PE = increase in KE

tiny-tim
Science Advisor
Homework Helper
Welcome to PF!

Hi physics10189! Welcome to PF! 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! 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

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)

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

yes because just before the blocks hit the ground can we assume that the height is zero therefore the PE final is zero???

What answer are you getting?

PhanthomJay
Science Advisor
Homework Helper
Gold Member

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