Question

A railroad car of mass 2.50∙10^4 kg is moving at a speed of 4.00 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 2.00 m/s.
(a)What is the speed of the four cars after the collision?
(b)How much kinetic energy is lost in the collision? Where does this energy go?

Answer 1

Answer:

a) v = 1.00 m/s

b) ΔKE = 150 kJ

Lost  energy makes heat, noise, vibration in the system

Explanation:

conservation of momentum

let m be the mass of one car

m(4.00) + 3m(0) = 4mv

v = 1.00 m/s

ΔKE = ½m(4.00)² + ½(3m)(0.00)² - ½(4m)(1.00)²

ΔKE = 8m + 0m - 2m = 6m J

ΔKE = 6(2.50e4) = 150 kJ