A blue puck with a mass of 4.50×10−2kg , sliding with a speed of 0.220m/s on a frictionless, horizontal air table, makes a perfectly elastic, head-on collision with a red puck with mass m_red, initially at rest. After the collision, the velocity of the blue puck is 6.00×10−2 m/s in the same direction as its initial velocitya) Find the velocity of the red puck after the collision.b) Find the mass m_red of the red puck.. Created by Paul Wall. science-mathematics-en - physics-en

♠ initial momentum mb*v0 =mb*vb +mr*vr final momentum, mb=0.0045kg, v0=0.22m/s, vb=0.06m/s; this is momentum conservation; ♣ elastic means energy conservation: 0.5mb*v0^2 =0.5mb*vb^2 +0.5mr*vr^2; take mr*vr from (♠) and put it here, thenmb*(v0^2 –vb^2) = mb*(v0-vb) *vr, thence ♦ vr=v0+vb =0.22+0.06 =0.28m/s; and mr=mb*(v0-vb)/vr == 0.0045*0.16/0.28 = 0.00257kg;