Question

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In a closed system with no friction, a red sphere of 2.5 kg stands stationary. A blue sphere with a mass of 5.8 kg approaches the first sphere with a speed of 4.1 m/s. The two collide. After the collision, the blue sphere begins moving forward with a speed of 1.3 m/s. What is the velocity of the red sphere after the collision?

Answer 1

Red sphere 2.5 kg stationary velocity after ?
Blue sphere 5.8 kg speed 4.1 m/s after collision speed 1.3 m/s
m1 = the mass of the blue sphere = 5.8 kg
m2 = the mass of the red sphere = 2.5 kg
v1 = initial velocity of the blue sphere before the collision = 4.1 m/s
v2 = initial velocity of the red sphere before the collision = 0 m/s
v'1 = final velocity of the blue sphere after the collision = 1.3 m/s
v'2 = final velocity of the red sphere after the collision = ?
Conservation of momentum
m1v1 + m2v2 = m1v1 + m2v2
(5.8)(4.1) + (2.5)(0) = (5.8)(1.3) +(2.5)(v2)
23.78 = 7.54 + (2.5)(v2)
Subtract 7.54 from both sides
16.24 = (2.5)v2
2.5 2.5
v2 = 6.5