Let the mass of each car be M.
v 44 ft/s
Conserve linear momentum:
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Now, the frictional force on the sliding cars will be 2Mgμ where μ is the coefficient of kinetic friction and g=32 ft/s2 is the acceleration due to gravity. Therefore, the work which the frictional force does as the cars stop is
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The cars begin (right after the collision) with an energy
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and end with zero energy So,
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so
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