Static frictions and moving boxes on top of a box

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The discussion revolves around solving a physics problem involving static friction and the motion of boxes on a cart. The user expresses confusion about the logic behind their solution to question 4, despite arriving at the correct answers. Participants emphasize the importance of applying Newton's second law (F = ma) to analyze the forces acting on both the box and the cart. The conversation clarifies that the acceleration of both the box and cart is the same, leading to a simplified relationship between the forces involved. Ultimately, the mass of the box does not affect the force exerted by the cart, which helps resolve the user's confusion.
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Homework Statement



http://www.screencast.com/users/trinhn812/folders/Jing/media/d77fab7d-ece6-4c9c-be65-bf41f94770fd

Homework Equations



I got the right answers doing the work shown, but I don't understand the logic of how I solved question 4.

The Attempt at a Solution

 
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hi okgo! :wink:

you need to use good ol' Newton's second law (F = ma) twice …

show us what you get :smile:​
 
hmm so far..
m= mass of box and M=mass of cart. I assume the acceleration of the box and cart is the same.

F(box)=force(friction)=umg=ma
ug=a

F(cart)=force done by you=Ma
Substitute ug=a into the equation.
u*g*M=Force so mass of the box doesn't matter?
 
okgo said:
F(cart)=force done by you=Ma

Is that for the cart M or for both M and m?
 
ohh I didn't include that. Thanks, it makes sense!
 
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