Sample Problem Force And Motion

Sample Problem Force And Motion

A constant horizontal force r; of magnitude 20 N is applied to block A of mass m” = 4.0 kg, which pushes against block B of mass = 6.0 kg. The blocks slide over a friction less surface, along an x axis.

SOLUTION: We shall first examine a solution with a serious error. then a dead end solution. and then a successful solution.

Successful Solution: The key idea here is that, because of the direction in which force is applied. the two form a rigidly connected system. We can relate the net force on the system to the acceleration of the system with Newton’s second law. Here, once again for the x axis, we can write that law as

(a) A constant horizontal force F"p is applied to block A. which pushes against block B, (il) Two horizontal forces act on block A: applied force F,p and force F4R from block B. (e) Only one horizontal force acts on block B: force r; from block
(a) A constant horizontal force F 
is applied to block A. which pushes against block B,Two
horizontal forces act on block A: applied force F,p and force F
from block B. (e) Only one horizontal force acts on block B:
force r; from block

 

 

 

 

SOLUTION: The Key Idea here is that we can relate the net force on block B to the block’s acceleration with Newton’s second law, Here we can write that law. still for components along the  axis.

1

 

 

 

 

Thus, force  is in the positive direction of the .r axis and has a magnitude .

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