a 20000 kg railroad car moving at 2 m/s in the +x-direction overtakes and collid

Question

a 20000 kg railroad car moving at 2 m/s in the +x-direction overtakes and collides with PHYS 1408 Principles of Physics l: Discussion Spring 2017 2nd Assignment Momentum collides with A 20,000 kg railroad car moving at 2 m/s in the +x-direction overtakes and completely a kg railroad car moving at 1 m/s in the +x-direction. They collide in a inelastic collision. 1. What is the final speed of the two cars (stuck together? energy? 2. What fraction of the initial kinetic energy is retained in the final kinetic (Explain why each equation is used, Show all your work) ao, a ookt after

Explanation / Answer

Apply conservation of momentum

m1 u1 + m2 u2 = ( m1+ m2) v

v= m1 u1 + m2 u2/ m1 + m2

= 20,000(2) + 50,000(1)/70,000

=1.28 m/s

initial kinetic energy

KEi = 1/2 m1 u1^2 + 1/2 m2 u2^2

= 1/2 ( 20000)(2)^2 + 1/2 ( 50000)(1)^2

=65000 J

KEf = 1/2 ( m1 + m2) v^2 = 1/2 ( 70,000)( 1.28)^2

=57344 J

KEi - KEf/KEi = 65000 J-57344 J/65000 = 0.117 or 11.7 %

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