How Is the Contact Force Between the 7kg and 11kg Blocks Calculated?

AI Thread Summary
To calculate the contact force between the 7kg and 11kg blocks when pushed with a 190N force, the total mass of the blocks is 39kg, resulting in an acceleration of 4.87 m/s². The force exerted by the 4kg block on the 7kg block is calculated as 170.52N, which acts to the left. The force exerted by the 7kg block on the 11kg block is then determined to be -204.12N, indicating a sign error in the initial calculations. The correct interpretation shows that the contact force between the blocks is directed to the right, aligning with the chosen coordinate system. Understanding the direction of forces and signs is crucial for accurate calculations in physics problems.
Nicolaus
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Homework Statement


You are pushing four blocks of masses 4, 7, 11, and 17kg positioned next to each other on a frictionless surface.
Find the force of contact between the 7 and 11kg blocks when you push the blocks with a 190N force to the left.
They are arranged as such: |17||11||7||4|


Homework Equations


F = 190N = (17+11+7+4)a
a = 4.87

The Attempt at a Solution


m4a = F - F7on4
F7on4 = 190 - (4x4.87) = 170.52N
F4on7 = -170.52N
m7a = F4on7 - F11on7
F11on7 = -170.52 - (7x4.87) = -204.12N
 
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You're making a sign error. Note that acceleration is to the left.
 
So F7on4 should be -170.52 given that I have chosen the left direction as positive?
 
Nicolaus said:
So F7on4 should be -170.52 given that I have chosen the left direction as positive?
Yes. F7on4 points to the right, which is negative in your convention.
 
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