Question

A block with mass m1 = 10 kg moving at 5 m/s collides with another block with mass m2 = 20 kg moving the other way at 1 m/s. The two blocks stick together after the collision.

(a) What is their common final velocity, ->vf ?

(b) What is the center of mass velocity, ->v_CM?

(c) What would this collision look like in the center-of-mass frame?

Answer 1

(A) This is an inelastic collision

m1v1 + m2v2 = ( m1 + m2) v

v = m1v1 + m2v2 / m1 + m2

v = 10 * 5 - 20 * 1 / 10 + 20

v = 1 m/s

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(B) Center of Mass Has a Constant Velocity During an Inelastic Collision.

so,

v_cm = 1 m/s

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(C) The center of mass of the two object combination does not accelerate. As the collision is taking place, it doesn't alter the motion of the center of mass