Question #37 in the multiple choice problem set doesn't seem like the answer is correct. If there were no current then yes, t=100m/1m/s=100s would be correct. However, there is a horizontal 2m/s current pushing the swimmer down stream. The swimmer will be swimming farther than 100 meters. Am I looking at this problem incorrectly?
Manuel, the way to look at this problem is to split it into x and y directions. x is the downstream direction, y is across the river. The only velocity in the y direction is the swimmer's trying to swim in the y direction. That's 1 m/s. The river is pushing him in the x direction at 2 m/s. So he's actually doing the square root of 5 m/s at an angle of 27 deg to the horizontal (x direction).
The time it takes the swimmer to get across the river is just the distance in they direction divided by the speed in the y direction which is the same whether there is a current or not. The swimmer will hit the opposite shore downstream due to the river velocity.
Robert Whitney - Yes, there is a different interactive software program that will work on your Mac for FREE, regardless of its operating system. It's called Promethean ActivInspire - Personal Edition. Some of the school districts that we work in NJ have this program, instead of SMART Notebook. Since the instructions that I have for the download & installation of this program include graphics and we can't include graphics in our comments, I'll send them to you via email. If any questions arise, feel free to reach out to me via email (audra@njctl.org).
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