(a) The speed of puck A before the collision is determined as 0.847 m/s.
(b) The change in the total kinetic energy of the system that occurs during the collision is 0.009 J.
The speed of puck A before the collision is calculated from the principle of conservation of linear momentum as follows;
m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
0.251u₁ + 0.371(0) = 0.251( -0.12) + 0.371(0.654)
0.251u₁ = 0.2125
u₁ = 0.2125/0.251
u₁ = 0.847 m/s to the right
Initial kinetic energy = ¹/₂ x 0.251 x (0.847)² + ¹/₂ x 0.371 x (0) = 0.09 J
Final kinetic energy = ¹/₂ x 0.251 x (-0.12)² + ¹/₂ x 0.371 x (0.654)² = 0.081 J
ΔK.E = 0.081 - 0.09 = 0.009 J ≈ 0 J
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