Pulley and Spring scales?

Question

A pulley is attached to the ceiling. Spring scale A is attached to the wall and a rope runs horizontally from it and over the pulley. The same rope is then attached to spring scale B. On the other side of scale B hangs a 120-N weight. What are the readings of the two scales A and B? The weights of the scales are negligible.

These are the choices I have narrowed it down to:
A.) A reads 0; B reads 120N
B.) Both scales read 120N
C.) A reads 120 N; B reads 0

Answer 1

Both scales read 120 N.

The string has a constant tension in it equal to 120 N.
Start with the scale on the wall. Since the string has the constant tension and the scale is fixed to the wall, there is 120N pulling the scale.

The hanging scale is the same, although conceptually you have to consider that the weight hanging down is pulling the scale, and that the tension in the string at the top of the scale behaves the same as a reaction force as if the scale were attached to the ceiling.

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Answer 2

answer : m = mass of crate = fifty 5.0 kg W = m x g W = fifty 5 x 9.80 one W = 539.fifty 5 Newton by way of fact the decrease scale has a examining of a hundred and twenty N, the top scale would have a examining of : top Scale examining = W - decrease Scale examining = 539.fifty 5 N - a hundred and twenty N = 419.fifty 5 N (answer)