A railroad freight car, mass 18000 kg, is allowed to coast along a level track a

Question

A railroad freight car, mass 18000 kg, is allowed to coast along a level track at a speed of 9 m/s. It collides and couples with a 50,000 kg loaded second car, initially at rest and with brakes released. What percentage of the initial kinetic energy in the 18000 kg car is preserved in the two coupled cars after collision? 14.4 % 122% 26.5% 72% 64.8% A ventilation fan with a moment of inertia of 0.64 kg-m^2 has a net torque of 0.22 N-m applied to it. It starts from rest, what angular momentum will it have 1 s later? 2.112 kg-m^2/s 0.96 kg-m^2/s 0.22 kg-m^2/s 0.1267 kg-m^2/s 0.64 kg-m^2/s

Explanation / Answer

m1/m2=v2/v1

m1=18000
m2=18000+50000=68000
v1= 9

v2 = m1v1/m2 = 2.38

KE1 = 0.5m1v1^2 = 729000 J
KE2 = 0.5m2v2^2 = 192589.6 J

192589.6 / 729000 = 0.28 = 28%

100 - 28 = 72% loss

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