Speed and Mechanical Energy Lost in Railroad Car Collision

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Homework Help Overview

The problem involves a collision between a moving railroad car and three other coupled cars, focusing on the conservation of momentum and the calculation of mechanical energy lost during the collision.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the conservation of momentum as a key principle in analyzing the collision, with one participant attempting to set up the momentum equation to find the final speed of the coupled cars.

Discussion Status

There is an ongoing exploration of the momentum conservation principle, with participants working through the setup of the equations needed to solve for the final speed and kinetic energy comparisons. A hint has been provided to guide the original poster's understanding of what is conserved in collisions.

Contextual Notes

Participants are navigating the problem without complete clarity on the energy loss aspect, and there is a noted typo in the equation setup that could affect the understanding of the solution process.

TrippingBilly
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A railroad car of mass 2.49 104 kg, is moving with a speed of 3.89 m/s. It collides and couples with three other coupled railroad cars, each of the same mass as the single car and moving in the same direction with an initial speed of 1.95 m/s.
(a) What is the speed of the four cars after the collision?
(b) How much mechanical energy is lost in the collision?

Sorry, but I have no idea about this problem :(
 
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Hint: What is conserved in any collision?
 
Momentum, so...

2.49e4 * 3.89 + 3*2.49e4 *1.95 = 4*4.29e4 * V

?
 
TrippingBilly said:
Momentum, so...

2.49e4 * 3.89 + 3*2.49e4 *1.95 = 4*4.29e4 * V
Right. Looks good, except for a typo. Once you solve for the final speed, you can figure out the initial and final kinetic energies and compare them.
 

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