Ok, I have a cart on a frictionless ramp (no incline) that is attached to a string that goes over a pulley (also assumed to be frictionless) to a small weight. The cart has a fan on it to mimic a friction force. I need to figure out how to set up the problem to find the tension in the string. How do I set this up? The formula that I have been using does not take into account the fan's acceleration.

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