A 0.5 kg ball moving at 4 m/s collides head-on and sticks to a 1.5 kg ball at rest. What is the speed of the combined mass after the collision?
Show the answer and explanation
Correct answer
A. 1 m/s
Principle or equation
Conservation of momentum: m1 v1 + m2 v2 = (m1 + m2) v'.
Why this answer is correct
Initial momentum = 0.5*4 + 1.5*0 = 2 kg·m/s. Total mass = 2.0 kg. v' = 2/2 = 1 m/s.
Example
A 1 kg object at 3 m/s hits a 2 kg object at rest and sticks: v' = (1*3)/(1+2) = 1 m/s.
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