Two 5-N boxes are attached to opposite ends of a spring scale and suspended from pulleys as shown.
-What is the reading on the scale?
A)0 N
B)2.5 N
C)5 N
D)10 N
E)25 N

Question

Two 5-N boxes are attached to opposite ends of a spring scale and suspended from pulleys as shown. 
-What is the reading on the scale?
A)0 N 
B)2.5 N 
C)5 N 
D)10 N 
E)25 N

Quizplus · Accepted Answer

The weight of each box is 5 N, so the total weight of the system is 10 N. However, since the boxes are attached to opposite ends of the spring scale, their weights will cancel each other out and the reading on the scale will be equal to the tension in the spring, which is also 5 N.

Two 5-N Boxes Are Attached to Opposite Ends of a Spring