1. The problem statement, all variables and given/known data Three blocks in contact with each other are pushed across a rough horizontal surface by a 75 N force as shown. The acceleration of gravity is 9.8 m/s2 . If the coefficient of kinetic friction between each of the blocks and the surface is 0.076, find the magnitude of the force exerted on the 3.5 kg block by the 4.1 kg block. Answer in units of N. 2. Relevant equations sum of Fy=N-mg=0 => N=mg sum of Fx= -fk=max fk=uN 3. The attempt at a solution I have no clue how to figure out the force just between those two block... Do I add the first two blocks together to act a one force against the third block?
You mean like m1+m2+m3=9.6 kg Then the forces acting in the y direction is N1+N2+N3 and (m1+m2+m3)g forces acting in the x direction is fk and F which fk=u*(N1+N2+N3) right?
so the sum of Fy= N1+N2+N3-Mg=0, where M is m1+m2+m3 so N1+N2+N3=Mg=> where N1+N2+N3=94.08 so the sum of Fx= -fk=Ma fk=u(N1+N2+N3) fk=7.15008 so -7.15008=9.6a a=-0.7448 m/s^2 this is small... is this right?
OK. ΣF = ma But ΣF ≠ -fk. Friction is not the only horizontal force acting. OK. No, as explained above.
Friction is one of the horizontal force acting on the blocks. What direction does it act? What other horizontal forces act? Look at your diagram.
Yes, but make sure you have the correction directions and thus the correct signs for the forces. (Hint: Let 'right' be positive and 'left' be negative.)
Looks fine to me. Why do you say it's wrong? Did the problem even ask you for the acceleration? (Finding the acceleration is just a step towards the required answer.)
That won't tell you anything about the forces between m2 and m3. Hint: Analyze m3 alone or m1 + m2 together.
So the only forces acting on m3 in the x direction is the force from m1 and m2... in the y direction it is N and m3g So for the force in the x direction from m1 and m2 (i'll call P12) F-P12=m3a? I'm not sure how to calculate P12...
No. What about friction? Which block is m3? Your diagram isn't labeled. OK. Once you account for all the forces, the only unknown will be the force between m2 and m3. You'll solve for it.
Sorry m3 is the right block i'm trying to figure out the right block and middle so if it is the right block does force even apply? so I did the sum of Fx = -P12-fk=m3a is that right?