Two springs of constants $k_1$ and $k_2$ connected in **series** have effective spring constant:
- $k_1 + k_2$
- $k_1 k_2 / (k_1 + k_2)$
- $k_1 - k_2$
- $\sqrt{k_1 k_2}$
Show answer and 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 $k_{eff} = k_1 + k_2$.