Correct option (b) (π+ 4)√(m/k)
Explanation:
The period of oscillation = 2π√(m/k)
⇒ The period of motion till the block is in contact with the spring
t1 = π√(m/k) then it leaves the spring with a speed v = ωA
Then it moves with constant velocity v for a distance D = l + l = 2l
⇒ The corresponding time of motion = t2 = 2l/v