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Date Posted: 4/2/2008 3:41:20 PM  Status: Live
PLEASE HELP, TEST TOMORROW!!! :-(
Course Textbook Chapter Problem
N/A N/A N/A N/A
Question Details:
 
Mass of block A is 4 kg, and Mass of  block B is 5 kg. 
 
There is no friction involved.
 
Question:  Use conservation of energy to find the velocity of the masses just before block B hits the floor.  The acceleration of the blocks is 3.1, masses are initially at rest.
 
I dont understand the solution which is:
 
Why is mA being multiplied by gh when gh is the height of Block B???
Alos why is mB Being multiplied by gh sinθ when that is the height of Block A??
Solution:
E1 = E2  -->  0 +mAgh = 1/2 (mA + mB ) v22 + mBgh sin θ

Answers:

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Date Posted: 4/2/2008 5:28:57 PM  Status: Live
Asker's Rating: Lifesaver   
Response:
 
Free body diagrams are shown in fig
the block A because there is no friction will have the force equation
the block B will have the equation
  adding these two equations T will be eliminatede
 Energy considerations
initially both blocks are at rest so the initial kinetic energy of the system is zero
initial potential energy of block B is
initial potential energy of block A is taken as zero
initial potential energy of system
final potential energy of block A is
final potential energy of block B is  when it reaches the ground
final Potential energy of system is
both the blocks move together so their final velocity  is the same
final kinetic energy of the system is
Initial total energy of system
final total energy of the system
as B descends by h , block A moves up the plane a distance L along the plane  and
In the problem ; ; h =  0.75m ; θ = 32
If you know L = ? we can find
Tako1985's Comment:
thank you!



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