Teaching Physics with the Physics Suite
Edward F. Redish
While walking by your friend’s dorm, she calls to you saying her door is stuck and she’s locked in but she needs to get out and get to class for her physics exam. You suggest she climb out the window, but the bottom of the window is too high up from the ground and she is afraid to jump. You note that there is a work site nearby with some rope and boards. You suggest that you can hook a loop of rope off a convenient gargoyle on one side of her window, put one end of a board in the loop, and hold the other end up for her. You could hold it about half wayup so she could lower herself down in two steps safely. This arrangement is sketched at the right.
She is heavier than you and you know you can’t hold up her weight by yourself. Estimate how long a board you need in order to be able to hold her up without dropping her. (The picture is drawn only to show the arrangement. The length of the board shown has not been adjusted to be appropriate.)
Be sure to clearly state your assumptions and how you came to the numbers you estimated, since grading on this problem will be mostly based on your reasoning, not on your answer.
Page last modified December 11, 2010: R29