Collision Conservation of Energy

[jakeginobi]

Homework Statement

a 5.0 x 10^5kg railroad car moving at 8.0m/s. collides with a stationary railroad car of equal mass. after the collision the two cars lock together and slide forward. What is the final velocity of the wrecked cars?
using conservation of energy
M1 = 5.0 x 10^5 kg
M2 = 5.0 x 10^5
Vi1 = 8.0m/s
Vi2 = 0m/s
Vf = ?

Homework Equations

Ek = 1/2mv^2

The Attempt at a Solution

I didn't know where to start, I found the kinetic energy of the railroad car(1.6 x10^7 J) and added it to the stationary one - since it's stationary the railroad car would initially have 0 kinetic energy

 

[jakeginobi]

My teacher didn't teach us how to solve collision questions using conservation of energy

 

[gneill]

What type of collision does this scenario represent? What's conserved and what's not conserved in such a collision?

 

[jakeginobi]

I believe it represents an elastic collision, and conservation of energy/momentenum is conserved. They both lock on together after collision and move as one.

 

[PeroK]

My teacher didn't teach us how to solve collision questions using conservation of energy

Earlier on today, it was conservation of momentum your teacher hadn't covered yet!

https://www.physicsforums.com/threads/collision-conservation-of-energy.860469/#post-5399283

 

[gneill]

I believe it represents an elastic collision, and conservation of energy/momentenum is conserved. They both lock on together after collision and move as one.

Review the properties of the collision types. You've got things backwards.