Two springs of constants $k_1$ and $k_2$ connected in **series** have effective spring constant:
A$k_1 + k_2$
B$k_1 k_2 / (k_1 + k_2)$
C$k_1 - k_2$
D$\sqrt{k_1 k_2}$
Answer & Solution
Correct answer: B. $k_1 k_2 / (k_1 + k_2)$
Series: $1/k_{eff} = 1/k_1 + 1/k_2$ ⇒ $k_{eff} = k_1 k_2/(k_1+k_2)$. (Series springs both stretch under same force, so total extension adds up — like resistors in parallel.) Parallel springs (both stretch the same amount) give $k_{eff} = k_1 + k_2$.
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