A hockey puck p₂ with a mass of 170 g is initially at rest. Another puck, p₁, with an unknown mass, is moving at an initial speed of 30 m/s. Puck p₁ collides with puck p₂​. After the collision, both pucks move in the same direction as puck p₁​ was originally moving. The collision causes puck p₂ to start moving at a speed that is half of the initial speed of puck p₁. The collision also causes the puck p₁ to slow down, and it moves at half its initial speed. What is the mass of the puck p₁?