Wednesday
May 4, 2016

# Homework Help: physics

Posted by physics on Wednesday, July 21, 2010 at 1:28pm.

A man (weighing 915 N) stands on a long railroad flatcar (weighing 2720 N) as it rolls at 18.5 m/s in the positive direction of an x axis, with negligible friction. Then the man runs along the flatcar in the negative x direction at 55.00 m/s relative to the flatcar. What is the resulting increase in the speed of the flatcar?
• physics - drwls, Wednesday, July 21, 2010 at 4:14pm

This is a conservation of momentum problem, but I think you have made an error in the runner's speed. No one can run 55 m/s. The world's fastest human, Olympic champion Usain bolt, runs 11 m/s at most.

• physics - physics, Wednesday, July 21, 2010 at 4:45pm

The problem has 55m/s... the instructor changed numbers in the original problem and I guess he wanted to change that number to 55. I thought it was strange too at first. So for conservation of momentum, would i use mhvh=mcvc where h is for human and c is for car?