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May 29, 2015

Posted by **Physics** on Sunday, July 12, 2009 at 6:48pm.

Three blocks on a frictionless horizontal surface are in contact with each other as shown in Fig. 4-5. A force F is applied to block 1 (mass m1). (a) Draw a free-body diagram for eeach block. Determine (b) the acceleration of the system (in terms of m1, m2, m3), (c) the net force on each block, and (d) the force of contact that each block exerts on its neighbor. (e) If m1 = m2 = m3 = 12.0 kg and F = 90 N, give numerical answers to (b), (c), and (d). Do your answers make sense intuitively?

Ok here's the free body diagram that i drew. The last one I drew was wrong... I guess...

|m1| this represents the block m1 same thing goes for m2 and m3

--- words ---> this is a force with the words being the name of the force

free body diagram of forces in the x axes

------ the Force F exerted by unknown object onto the first block ------> <-------- Reaction force exerted by block onto the unkown object that applied the force ------- | this is the first block with mass m1 | --- contact force exerted by the first block onto the second ----- > <------ the reaction force exerted by the second block onto the third ------ | this is the second block with mass m2 |-------contact force exerted by the second block onto the third--------> <------This is the reaction force exerted by the third block onto the second ------- |this is the third block with mass m3 |

Is this free body diagram correct????

I understand that mass and force don't add up that's because this is the free-body diagram of the situation not the mathamatical relationship. Is this free body diagram correct?

Ok I can find the acceleration and do part (b) ok

defintion of net force = m a

cancel out the mass for the acceleration

(defintion of net force = m a)m^-1 = a = m^-1 net force

this gave me

a = m^-1 net force

plug in mass for whole unit

a = m^-1 net force = (m1 + m2 + m3)^-1 net force

this is what I got

a = (m1 + m2 + m3)^-1 net force

ok part c

I have no idea how to do because I think my free body diagram is wrong can you please tell me how to fix my free body diagram that way I can make sense of the answers you have given me.

ok part d

I have no idea how to do because I think my free body diagram is wrong can you please tell me how to fix my free body diagram that way I can make sense of the answers you have given me.

part e

I believe I can do this once I have figured out how to do the rest of the problem and dosen't need to be explained to me

THANKS!

- Physics -
**bobpursley**, Sunday, July 12, 2009 at 8:03pmAt the college bookstore, or Barnes Noble, you can find Schaum's Outline Series, College Physics, in which problems such as this are detailed in solution. I recommend it to you.

Now. If F (90N) is pushing on M1, which is pushing also M2 and M3, and the acceleraltion is then 90/(12+12+12), that gives the acceleration of the system as 2.50/s^2

Now, if m3 is accelerating at 2.50m/s^2, the force pushing it (F3) has to be ma or 12*2.50=30N.

Now if some force F2 is pushing m2 and m3, then it must be (12+12)2.50=60N

And as a check, the force pushing F1 accelerates all three blocks, F1=(3*12)2.5=90N