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Beginner question here. Also, English isn't my first language, but I will try to make this somewhat readable.

Lets say that you are holding onto a rope that is tied to a sledge. Your weight is 76 kg and sledge is 200 kg. Using the rope, you start pulling yourself towards the sledge and the force you use to do this is 120N. Since the sledge is heavy, it will start to slide and accelerate towards you at a very slow pace (a = F/m = 120N/200kg = 0,6 m/s^2).

Now by Newton's 3rd law: "If an object A exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A." Would it mean that the force exerted by the rope that's tied to the sledge is equal to the force that you are using to pull yourself towards the sledge? So you would be accelerating towards the sledge at a = F/m = -120N /76 kg = -1,6 m/s^2 (acceleration is negative, since compared to the sledge you are moving to the opposite direction)?

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1 Answer 1

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Welcome to Physics StackExchange!

If both you and the sledge are on a frictionless surface, and the rope is massless, then yes, your application of Newton's third law is correct, you will accelerate towards the sledge at 1.6 $m/s^2$.

If you are on rough ground (but the sledge is on a frictionless surface), then the ground exerts the same magnitude of force but at an opposite direction to the tension, such that the net force on you is zero; then you won't move.

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  • $\begingroup$ Yup, there is no friction or mass for the rope. Thank you! $\endgroup$ Commented Jan 13, 2020 at 17:01
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    $\begingroup$ he meant friction in the floor $\endgroup$
    – user65081
    Commented Jan 13, 2020 at 18:07
  • $\begingroup$ @Wolphramjonny I have modified my response and addressed the case when there is friciton on the floor for the person. $\endgroup$
    – Leo L.
    Commented Jan 14, 2020 at 2:07

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