January 18, 2007 by guestauthor in
Open for interpretation. Obviously the teacher did not appreciate the humor in this particular students answer. Thanks Syl.
He didn’t say a or b. He should have said b first.
That is exactly the kind of answer I used to give in physics exams as well. I couldnt care less how fast some apple drops down from the tree, I’m just happy to know it drops…
Let the people who are interested waste their life on such questions…
PS. I still managed to get past physics course…
I don’t see the comedy in the answer. Are elephants that funny?
I would have given that kid full marks. With an elephant in the way, of course it wouldn’t!
Energy at top of ramp -> mgh = 3 kg * 9.8 m/s**2 * 5 m
Energy put into the spring -> (1/2)kx**2 = 50 N/m * x**2
[The student was on the right track up to here.]
When it stops, the block has no kinetic energy, and E sub i = E sub f, therefore mgh = (1/2)kx**2 -> 147 = 50x**2 -> x = sqrt(147/50) = 1.71 meters. (Note that there is no friction in this system. Makes things easier.)
Since there’s no friction, the same energy put into the spring pushes it back up to the top of the ramp where it initially came from, so it goes back up 5 m to where it started.
So the elephant would fall, because there is no friction….??
^Hehe, he wouldn’t need friction to stand, just to move ;)
You wouldn’t be able to solve this anyway because there’s too little information. There is no mention that this is on Earth, so choosing earth’s gravitational constant doesn’t work. There is a mention that the ramp is frictionless, but no mention of air friction (or lack therof).
Although, last I checked, elephants were only found on Earth.
the answer is obviously clipped off and the assumption that, yes, this occurs on earth is pretty obvious. Also this is most certainly from an intro physics course, which doesn’t delve into such factors as air resistance.
I’d have given the kid full marks but the question states that the object does compress the spring, so obviously to do that it had to get to the spring. So the elephant excuse, while good for a chuckle, is out of the parameters given by the question. So yeah, I’d have given it a 0 too :P
I’d have answered that there is no such thing as a frictionless ramp,drawn an arrow toward the little x and pointed out that after it had come to a rest it wasn’t moving anymore.
And I’d have got a zero,I’m sure.
This elephant is flying and obviously has no effect on the box dropping. Its no wonder he failed. I don’t know why the elephant stumped him, the math is on the right track.
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