## Question

Figure shows three identical springs A, B, C. When a 4 kg weight is hung on A, it descends by 1 cm. When a 6 kg weight is hung on *C*, it will descent by

### Solution

3.0 cm

Let k be the force constant of each spring. The force *F* needed to extend the spring *A* by an amount *x* is

In figure b, the springs are connected in series. Therefore, the force constant *k**’* of the combination is given by

If a force *F**’* is applied, the combination will extend by

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