A railroad diesel engine weighs four times as much as a freightcar. If the diesel engine coasts at 5km/h into a freightcar that is initially at rest, how fast do the two coast after they couple together?(adsbygoogle = window.adsbygoogle || []).push({});

Given:

m1= 4m2

m2

v1=5km/h

v2=0

unknown : v3

formula:

m1v1+ m2v2=m3v3 (i.e., Total momentum before=total momentum after)

work:

m1v1+ m2v2=m3v3 --> (4 x m2)(5km/h) + (m2)(0)=m3v3

(20km/h)m2=m3v3

answer --> 20km/h=v3

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Railroad diesel engine homework

**Physics Forums | Science Articles, Homework Help, Discussion**