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Work done on the block by force

by Zmuffinz
Tags: block, force, work
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Zmuffinz
#1
Jul23-09, 06:17 AM
P: 6
1. The problem statement, all variables and given/known data

A block is pushed across a rough horizontal surface from point A to point B by a force (magnitude P = 5.4 N) as shown in the figure. The magnitude of the force of friction acting on the block between A and B is 1.2 N and points A and B are 0.5 m apart. If the kinetic energies of the block at A and B are 4.0 J and 5.6 J, respectively, how much work is done on the block by the force P
between A and B?


2. Relevant equations
W= PCos (theta)D


3. The attempt at a solution
I have no idea what to do for this!
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songoku
#2
Jul23-09, 06:33 AM
P: 767
I suppose Work done on the block = change in kinetic energy + work against friction
tiny-tim
#3
Jul23-09, 07:00 AM
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tiny-tim's Avatar
P: 26,157
Hi Zmuffinz! Welcome to PF!

(have a theta: θ )
Quote Quote by Zmuffinz View Post
W= PCos (theta)D

I have no idea what to do for this!
Well, what is θ in this case?

Zmuffinz
#4
Jul25-09, 06:19 AM
P: 6
Work done on the block by force

well you see thats why im stuck, i wasnt given an angle, or mass of the block or anything so ive got no clue as to what to do:(
Zmuffinz
#5
Jul25-09, 06:20 AM
P: 6
Quote Quote by songoku View Post
I suppose Work done on the block = change in kinetic energy + work against friction
and how do i calculate work against friction?
Doc Al
#6
Jul25-09, 07:15 AM
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P: 41,310
Quote Quote by Zmuffinz View Post
well you see thats why im stuck, i wasnt given an angle, or mass of the block or anything so ive got no clue as to what to do:(
You didn't post the diagram, but I presume that the force was applied horizontally. That will tell you all you need about angles.


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