Two railroad freight cars with masses 130 Mg and 170 Mg approach with equal spee

Question

Two railroad freight cars with masses 130 Mg and 170 Mg approach with equal speeds of 0.330 m/s . They collide, the lighter car rebounding opposite its original direction at 0.290 m/s .

A. Find the velocity of the heavier car after the collision. Assume the original direction of the lighter car is positive. Express your answer to two significant figures and include the appropriate units.

B.What fraction of the original kinetic energy was lost in this inelastic collision? Express your answer using two significant figures.

Explanation / Answer

(A)

By conservation of momentum:

130*0.33-170*0.33 = -130*0.29+170*V

-13.2 = -37.7 + 170*V

V = (37.7-13.2)/170

V = 0.144 m/s

V = 0.14 m/s [opposite to original direction]

(B)

KE(lost) = [(0.5*(130+170)*0.33^2) -(0.5*130*0.29^2)-(0.5*170*0.144^2)]*9.8

= 89.24 J OR 89 J

Fraction = 89/([0.5*(130+170)*0.33^2*9.8)

= 0.556

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