Incredibly complicated for basic physics

AI Thread Summary
The discussion revolves around a physics problem involving a book on a table, where a person applies forces to maintain constant speed. The key challenge is calculating the horizontal force exerted by the left hand while accounting for the coefficients of kinetic friction and the normal force. Participants emphasize the importance of recognizing that constant speed implies zero acceleration, simplifying the force balance equation. The solution involves summing the forces and considering the frictional forces acting on the book. Ultimately, the problem was resolved with guidance on applying the correct physics principles.
JAK3CAL
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Homework Statement




You place a book flat on a table and press down on it with your right hand. The hand-to-book and table-to-book coefficients of kinetic friction are 0.47 and 0.44 respectively. The book's mass is 0.84 kg and your downward push on it is 9.00 N. Now, you use your left hand to push the book along the table at constant speed. Assuming that your right hand is stationary with respect to the table, what is the horizontal force exerted on the book by your left hand?


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The Attempt at a Solution



think its got something to do with the fact that the two friction coefficients are like a sandwich on the book. the x direction equation is the force you push the book with minus the two frictions added together= mass times acceleration but I can't get it to work. HELPPPPPPPPPPPPPPP I've spent an hour on this any push in the right direction is appreciated before I lose my damn mind
 
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JAK3CAL said:
the x direction equation is the force you push the book with minus the two frictions added together= mass times acceleration
Yes, that much is correct. But don't forget the problem statement says, "use your left hand to push the book along the table at constant speed." What is the acceleration of something moving at a constant velocity?

You've mentioned that you've worked on this for an hour. So show us your work! :smile: Maybe we can help you once we see what you've done specifically, and where you are stuck.
 
You must remember that kinetic friction has a dependence of the Normal Force (N). So if you sum the forces in the x direction you get :

Fx = Fh - Fk= ma; (Fh = Force by hand; Fx = force of friction) what is acceleration if it is constant?Kinetic Friction is =\muk*NYou can now plug in your frictional force, and solve for the force due to your hand
 
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Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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