Answer to Question #250976 in Physics for Pranali

Question

Two blocks with masses m₁ = 1.7 kg and m₂ = 4.6 kg are at rest on a frictionless surface with a compressed spring between them. The spring is initially compressed by 72.0 cm and has negligible mass. When both blocks are released simultaneously and the spring has dropped to the surface, m₁ is found to have a speed of 2.1 m/s. What is the speed of m₂?

Answer 1

The spring here is just a factor that makes the blocks move. Since we know the speed of the one block and the mass of both blocks, we can apply momentum conservation to find the speed of the second block:

$$0=m_1v_1-m_2v_2,\\\space\\ v_2=v_1\frac{m_1}{m_2}=0.78\text{ m/s}.$$