John Cook over at the Endeavour wrote a quick blog about a homework conversation with his daughter about physics homework:
My daughter and I were going over science homework this evening. A ball falls for 10 seconds. What is its final velocity?
JC: So how fast is the ball going when it hits the ground?
RC: Zero. It stops before it bounces back up.
JC: Well, how fast is it going just before it hits the ground?
RC: They didn’t ask the almost final velocity. They asked for the final velocity.
It reminded me of a two students working on a related rates problem in class,
It was a typical -------A 6 foot tall man is walking away from a 15 foot tall lamppost at a ......find the rate at which his shadow is growing.
After about ten minutes of the one who "got it" trying to explain, they called me over.
So I asked, "Have you drawn a picture?"
She replies, "That's the problem, how can you draw a picture if you don't know where the sun is at?"
Me, confused, "????" THE SUN???
Her.." Yes, the shadow will depend on the angle of the sun won't it?
ME.....OHhhhhhhhhhh.... OK... It's night-time... now read the problem....
HER... read...mumble,,, read... OHhhhh...... why didn't they say that...