Two 50-N weights pull on the scale as shown. The reading on the ...

[Mimi]

Two 50-N weights pull on the scale as shown. The reading on the scale is
 
  1) 0 N.
  2) 25 N.
  3) 50 N.
  4) 100 N.
 
  This is clearer to understand if we think of the situation this way:
  5) Since no acceleration is taking place, the forces cancel one another.
  6) One of the weights holds the scale while the other weight stretches the spring.
  7) The two hanging weights provide forces that constitute an action/reaction pair.

Question 2

The two men compete in a tug of war. Both pull equally and the scale reads 800 newtons. Each man must pull with a force of
 
  1) 400 N.
  2) 800 N.
  3) 0 N.
 
  Consider action and reaction forces in this case: If action is the man on the left pulling on the rope, then the reaction force is
  4) the rope pulling on the man on the left.
  5) the rope pulling on the man on the right.
  6) the man on the right pulling on the rope.

[mceravolo]

Answer to Question 1

Answer: 3, 6

Answer to Question 2

Answer: 2, 4