A loaded runaway railway wagon with a mass of 20 tonnes travelling at 15kmh-1collides with an empty

Fantastic news! We've Found the answer you've been seeking!

Question:

A loaded runaway railway wagon with a mass of 20 tonnes travelling at 15kmh-1collides with an empty stationary wagon with a mass of 4 tonnes. If the two wagons couple together on impact and there are no losses, at what speed in kmh-1will the coupled wagons be travelling?Use sketches to show the wagons before and after impact