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Physics/Newtons Law Problem

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Question
Three blocks, with masses m1 = 5.90 kg, m2 = 5.50 kg, and m3 = 7.10 kg, are pull on a horizontal frictionless surface by a 18.00 N force that makes a 39 o angle (θ) with the horizontal (see figure). What is the magnitude of the tension between the m2 and m3 blocks?

https://general.physics.rutgers.edu/gifs/CJ/4-44.jpg

Answer
Hello Neal,

The applied force is not horizontal, so we need to calculate what component of the 18 N is in the horizontal direction.
F_horiz = 18.00 N*cos39 = 13.99 N

The sum of the 3 masses to be accelerated is 18.5 kg. They will accelerate according to Newton's 2nd Law:
F = m*a so in this case
a = F_horiz/m = 13.99 N/18.5 kg = 0.7562 N/kg = 0.7562 m/s^2

So what is the tension in the cord pulling m3? It is enough to accelerate a 7.10 kg mass at a rate of 0.7562 m/s^2.

You can do the rest of this! Use Newton's 2nd again, where this time F is the tension, T, and m is the mass m3.

I hope this helps,
Steve

Physics

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Steve Johnson

Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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