An electron with a speed of 3.0 × 10⁶ m/s collides with an atom which has the following energy levels: n₁ = -24.6 eV, n₂ = -5.4 eV, and n₃ = -2.4 eV. The atom emits a 619.9 nm photon after the collision. Ignoring the atomic recoil, since the atom's mass is significantly larger than the electron's mass, determine what the electron's final speed will be. Note that the photon energy ≠ collision energy.

Determine the combined speed immediately after a collision where a 131-kg robot, moving at 2.6 m/s, collides head-on with (and holds on to) an 83-kg drone moving at 5.1 m/s towards the robot.

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?