Force Exerted by Blocks on a Frictionless Surface

AI Thread Summary
A rightward force of 14 N is applied to a series of blocks with masses of 5 kg, 10 kg, and 25 kg on a frictionless surface. The acceleration of the blocks is calculated to be 7/15 m/s², based on the total mass of 40 kg. The force exerted by the middle block on the rightmost block is confirmed to be approximately 8.75 N. The discussion also seeks to determine the force that the leftmost block exerts on the middle block, as well as the effects of reversing the order of the blocks. The calculations rely on Newton's second and third laws of motion.
farrah003
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1. Homework Statement

Blocks of mass 5, 10, and 25 kg are lined up from left to right in that order on a frictionless surface so each block is touching the next one. A rightward-pointing force of magnitude 14 N is applied to the left-most block.

a) What is the magnitude of the force that the middle block exerts on the rightmost one?
Fright, middle = 8.749999995
b) What is the magnitude of the force that the leftmost block exerts on the middle one?
Fmiddle, left = ?
c) Suppose now that the left-right order of the blocks is reversed. Now find the magnitude of the force that the leftmost block exerts on the middle one?
F'middle, left = ?


i figured out the first part i just need help to do the last two
 
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I don't think (a) is right. Here's what I would do.

F = ma

The force pushing on the blocks is equal to their total mass times their acceleration but we have to solve for acceleration.

14 = 30a

a = 7/15

Use F = ma for every question and don't forget Newton's 3rd law
 
part a is correct because the homework is on a software and it accepted my answer
 
how did you get a
 
Nevermind. I screwed up. The total mass of the blocks is equal to 40 not 30. So a is right.
 
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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