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A $ 2.0 kg $ block is being pulled across a frictionless table by a rope with negligible mass at an angle $ \theta=60° $ (from positive direction of $ x $ axis, we have taken horizontal surface of table as $ x $ axis) The tension in the rope is $ 12N $ and causes the box to slide across the table to the right with an acceleration of $ 3.0 m/s² $ But the direction of net force is along the rope. The direction of acceleration isn't. Why is that? There is a net vertical force and that force is vertical component of tension force. The gravitational force is balanced by the normal force (the magnitude of normal force and gravitational force are always same). Why is the acceleration only along horizontal component of tension force. It should be along the the net tension force (along the rope)

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marked as duplicate by M. Enns, ZeroTheHero, Gert, Community Jan 20 at 17:32

This question was marked as an exact duplicate of an existing question.

  • $\begingroup$ Almost identical question $\endgroup$ – Farcher Jan 20 at 11:20
  • $\begingroup$ Te reaction force isn't just there to resist gravity, the surface will react to whatever force is exerted on it. With a component of the tension going upwards against the weight of the block, the force exerted on the surface and therefore the reaction force is less. $\endgroup$ – cal Jan 20 at 11:21
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The acceleration is always in the direction of the net force (Newton's Second Law). In your example, if you simply resolve all the forces in the vertical and horizontal directions, you can see why.

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The basic assumption here is that the gravitational force is balanced by both the normal reaction from the table and the tension component in the vertical direction. As there is now a horizontal force along the table, it accelerates as such.

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