The dynamometer will show the force F = 20 N.
According to Newton’s 3 law: the force F12, with which 1 body acts on 2, is equal in modulus to the force F21, with which 2 the body acts on 1, and is oppositely directed.
F12 = – F21.
The dynamometer acts only as an intermediate link between the forces F12 and F21, through which one body transfers its impact to another body.
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