Question
What will be the force constant of the spring system shown in figure?
A.
$$\frac{{{k_1}}}{2} + {k_2}$$
B.
$${\left[ {\frac{1}{{2{k_1}}} + \frac{1}{{{k_2}}}} \right]^{ - 1}}$$
C.
$$\left[ {\frac{1}{{2{k_1}}} + \frac{1}{{{k_2}}}} \right]$$
D.
$${\left[ {\frac{2}{{{k_1}}} + \frac{1}{{{k_2}}}} \right]^{ - 1}}$$
Answer :
$${\left[ {\frac{1}{{2{k_1}}} + \frac{1}{{{k_2}}}} \right]^{ - 1}}$$
Solution :
Two springs of force constants $${{k_1}}$$ and $${{k_1}}$$ are in parallel. Hence
$$k' = {k_1} + {k_1} = 2\,{k_1}$$
The third spring $${k_2}$$ is in series with spring of force constant $${k'}.$$
$$\therefore \frac{1}{k} = \left[ {\frac{1}{{2{k_1}}} + \frac{1}{{{k_2}}}} \right]\,\,{\text{or}}\,\,k = {\left[ {\frac{1}{{2{k_1}}} + \frac{1}{{{k_2}}}} \right]^{ - 1}}$$