(a) A 10-kg block is supported by cord that runs to a spring scale, which is supported by another cord from the ceiling as shown in fig. What is the reading on the scale?

(b) In Fig. the block is supported by a cord that runs around a pulley and to a scale. The opposite end of the scale is attached by a cord to a wall. What is the reading of the scale?

(c ) In fig. the wall has been replaced with a second 10-kg block, what is the reading on the scale now?
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Explanation

In all the three cases the spring balance reads 10 kg.
Let us cut a section inside the spring as shown in fig

As each part of the spring is at rest , so `F=T`. As the block is stationary, so `T=F=100N`.