Freight car-caboose collision finding mass without velocities

In summary, the freight car and caboose car collided, and 23% of the initial kinetic energy was dissipated as heat, sound, vibrations, and so on. The caboose has a mass of 34,000 kg.
  • #1
hangten1039
17
0
A 34000-kg railroad freight car collides with a stationary caboose car. They couple together, and 23 percent of the initial kinetic energy is dissipated as heat, sound, vibrations, and so on. What is the mass of the caboose?



m1v1= (m1+m2)vf
KEbefore= .23KEcollision

I don't know how to set up the last equation so that velocities cancel. I am not sure how to set up the kinetice energy equation, please help! thank you!
 
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  • #2
hangten1039 said:
m1v1= (m1+m2)vf
OK.
KEbefore= .23KEcollision
Rethink this one more carefully.

I don't know how to set up the last equation so that velocities cancel. I am not sure how to set up the kinetice energy equation, please help!
What's the definition of KE? Write vf in terms of v1 (using your first equation).
 
  • #3
so would i get for kinetic equation:
.5m1(v1^2)= .23(.5)(m1+m2)(m1v1/(m1+m2))
 
  • #4
nevermind i would actually get: .5(m1)((m1+m2)(vf)/m1) = .23(.5)(m1+m2)vf
 
  • #5
hangten1039 said:
so would i get for kinetic equation:
.5m1(v1^2)= .23(.5)(m1+m2)(m1v1/(m1+m2))
Two problems:
(1) You forgot to square the velocity on the right hand side.
(2) The final KE is less. If 23 % of the initial KE is "lost", what's left?
 
  • #6
I'm not sure I understand what you are explaining in part 2..

so my equation would be .5m1(v1^2)= .23(.5)(m1+m2)(m1v1^2/(m1+m2))
 
  • #7
I still have initial velocity as unknown or final velocity, so I'm not sure how to get rid of that
 
  • #8
hangten1039 said:
I'm not sure I understand what you are explaining in part 2..

so my equation would be .5m1(v1^2)= .23(.5)(m1+m2)(m1v1^2/(m1+m2))
You still have the square wrong on the RHS. The entire vf term must be squared.

Your equation (once you correct the above error) says that the initial KE = 23% of the final KE. Does that make sense?
 
  • #9
hangten1039 said:
I still have initial velocity as unknown or final velocity, so I'm not sure how to get rid of that
Once you get the KE equation correct, the velocity cancels.
 
  • #10
so actually I would have to take 23% of the initial kinetic energy
 
  • #11
hangten1039 said:
so actually I would have to take 23% of the initial kinetic energy
You start with one dollar, but then lose 23 cents. What's left?

So the final KE is what percentage of the initial?
 
  • #12
the final is 77% of the initial
 
  • #13
hangten1039 said:
the final is 77% of the initial
Good. Use that to write your KE equation.
 

What is a freight car-caboose collision?

A freight car-caboose collision is an accident that occurs when a freight car, which is a large, heavy railcar used for transporting goods, collides with a caboose, which is a smaller, lighter railcar that traditionally served as the last car on a train.

Why is it important to find the mass of the objects involved in a freight car-caboose collision?

Finding the mass of the objects involved in a collision is important because it helps determine the force of impact and the damage caused. It also plays a crucial role in understanding the physics of the collision and can aid in preventing similar accidents in the future.

How can the mass of the objects involved in a freight car-caboose collision be found without knowing their velocities?

The mass of the objects involved in a collision can be found by using the principle of conservation of momentum, which states that the total momentum of a system remains constant in the absence of external forces. By measuring the momentum of each object before and after the collision, the mass can be calculated.

What other factors need to be considered when determining the mass of the objects in a freight car-caboose collision?

In addition to momentum, other factors that need to be considered when determining the mass of the objects in a collision include the angle of impact, the coefficient of restitution (a measure of the objects' elasticity), and any external forces acting on the objects during the collision.

How can the results of a freight car-caboose collision mass calculation be used?

The results of a freight car-caboose collision mass calculation can be used to analyze the severity of the collision, identify any potential safety hazards or design flaws, and inform future safety measures and regulations for rail transportation.

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