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**1. 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 = ?

**2. Homework Equations**

Ek = 1/2mv^2

**3. 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