Mechanics help !

  • #1
Mechanics help :(!

I REALLY NEED HELP :(
Two blocks are connected by a cord which passes over a frictionless pulley at D.
Block A has a mass of 40 kg and block B a
mass of 120 kg. A rests on a horizontal
surface, while B rests on a ramp with the slope
shown. B is initially in a position 3 m from the
stop C as shown. The coefficient of kinetic
friction between the blocks and the surface
beneath is μK = 0.20 for both A and B.

(a) Find the acceleration of the two blocks and
the tension T in the cord, assuming that the
blocks just begin to move at time t = 0.
 

Answers and Replies

  • #2
993
13


Diagram?
 
  • #4
993
13


First we draw the FBD for mass A and for mass B.

How many forces act on each?
 
  • #5


on mass 1 we have forcetension - forcefriction + m*g = ma
mass2 -frocetension-Forcefriction2+(m*g)sin theta= m2a

the thing thats confusing me is if we could have assumed that the aceleration of B is same as acceleration of a before it hits the barrier in the diagram
 
  • #6
993
13


on mass 1 we have forcetension - forcefriction + m*g = ma
mass2 -frocetension-Forcefriction2+(m*g)sin theta= m2a

the thing thats confusing me is if we could have assumed that the aceleration of B is same as acceleration of a before it hits the barrier in the diagram
To avoid confusion, instead of mass 1 let us call it mass A as in diagram.

Re 1st equation: I do not know why you have m*g.

Until mass B hits the barrier at C we HAVE TO assume that the acceleration of B is the same (in magnitude) as that of A because otherwise the string either snaps or becomes slack and so there would not be any tension at all!
 

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