In the image, sir is saying that block will move with wedge with same acceleration (a) as wedge. The friction over all surface is 0. Also he says that block will slide towards bottom left with acceleration b. How can the block move left with same acceleration (a) with wedge as it has only one single force mg towrds bottom in its FBD?

							
The normal reaction force is also acting on the block
 
 
 
 
 
 
 
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