A 4 kg block moving at 10 m s⁻¹ strikes a spring of constant π² N m⁻¹ attached to another 4 kg block at rest on a smooth floor. The time for which the rear moving block remains in contact with the spring is:

Question

G1 Physics · Accepted Answer

During contact, use relative motion of the two equal 4 kg blocks. Reduced mass μ=2 kg and spring constant k=π² N m⁻¹, so relative angular frequency ω=√(k/μ)=π/√2. Contact starts and ends when the spring is at natural length, which takes half a relative oscillation: Δt=π/ω=√2 s. Correct answer: A.