Friends burt and ernie stand at opposite ends of a uniform log that is floating in a lake. the log is 3.0 m long and has mass 20.0 kg. burt has mass 30.0 kg; ernie has mass 40.0 kg. initially, the log and the two friends are at rest relative to the shore. burt then offers ernie a cookie, and ernie walks to burt's end of the log to get it. relative to the shore, what distance has the log moved by the time ernie reaches burt? ignore any horizontal force that the water exerts on the log, and assume that neither friend falls off the log.