Question

In scenario 1, a person pulls with a force F on a string of length 2d that is connected to a spring scale. The other end of the spring scale is connected to a post by a string of length d . In scenario 2, the person pulls on the string of length 2d with a force of F , and a second person stands where the post was in scenario 1, and also pulls with a force of F . If the spring scale reads 50 N in scenario 1, what does the spring scale read in scenario 2?

• A. 50 N
• B. 67 N
• C. 100 N
• D. 133 N
• E. 150 N

Answer 1

The correct option is A 50 N

In both cases, the spring scale isnt moving, which means that the net force acting on it is zero. If the person in scenario 1 is pulling the spring scale to the right with force F , then there must be a tension force of F in the string attaching the spring scale to the post in order for the spring scale to remain motionless. That means that the same forces are acting on the spring scale in both scenarios, so if the spring scale reads 5 0 N in scenario 1, then it must also read 5 0 N in scenario 2. Dont be fooled by the lengths of the pieces of string. Length has no effect on the tension force in a string.