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The only partial solution - partial because there are no magic bullets in physics teaching, just ways of attaining incremental improvements - is to make practice seem like a game. Scrimmage every day. Make the pitcher experience the consequences of walking back-to-back hitters during practice. Let them fail! Then, when the game comes, small failures are less likely to produce downward spirals.
In physics, I give quizzes like this every single day, with no questions allowed, and a strict time limit. That means lots of chances to screw up - good! Because everyone is used to communicating their knowledge (or lack thereof) under pressure. Then the AP exam doesn't feel as much like a high stakes event, but rather like just another day at the office.
FUNDAMENTALS CHECK 6:
51. Write the equation for the potential energy stored in a spring
52. Two carts collide and stick together. (a) Was momentum conserved in the collision? (b) Was mechanical energy conserved in the collision?
53. Two carts collide and bounce off one another. (a) Was momentum conserved in the collision? (b) Was mechanical energy conserved in the collision?
54. Define the period of simple harmonic motion.
55. Planet X has a gravitational field that is 1/8 that on earth. Joel has mass 100 kg on earth. What is his mass on Planet X?
56. What is found by the area under a force vs. displacement graph?
57. A system consists of two objects, and experiences no net external force. Describe the motion of the system's center of mass.
58. An object experiences only two forces: 20 N to the east, and 20 N to the north. What is the magnitude of the net force on the object?
59. What are the units of rotational kinetic energy?
60. Sketch a free body diagram for a car that is moving to the right and skidding to a stop.
Solutions to fundamentals check #6:
ReplyDelete51. (1/2)kx^2.
52. yes; no. (Momentum is always conserved in a collision; mechanical energy is only conserved in an elastic collision, and when objects stick together, the collision may never be elastic.)
53. yes; we don't know. (Momentum is always conserved in a collision. Mechanical energy would be conserved if the collision is elastic. We don't know whether or not the collision is elastic! Yes, in an elastic collision objects must not stick together, but not all collisions where objects bounce off one another are elastic. Either we have to be told explicitly that a collision is elastic, or we have to do a calculation comparing mechanical energy before and after collision to show the collision to be elastic.)
54. the time for the object to complete one cycle of harmonic motion.
55. 100 kg. (Mass is the amount of material contained in an object, which doesn't change based on gravitational field.)
56. work.
57. the center of mass moves at constant velocity. (No net external force means the system has no acceleration by F = ma, and no acceleration means no change in velocity for the system's center of mass.)
58. 28 N, or 20-root-2 N. (Force is a vector quantity, so perpendicular forces add using pythagoras.)
59. joules. (ALL forms of energy have units of joules.)
60. You should have drawn an upward arrow for the force of the road on the car (i.e. the normal force); you should have drawn a downward arrow for the force of the earth on the car (the weight); and you should have drawn a leftward arrow for the force of the road on the car (i.e. the friction force). There should be no arrow to the right - motion is not a force.
Greg, while I agree with your response for 55 for a physical science class, and possibly for a college-prep physics class in a physics-first curriculum (which I believe is what Woodbury does), if the students have had chemistry, I think the distinction needs to be made that mass is the measurement of an object's inertia, while moles is the amount of substance in an object.
ReplyDeleteNo, we didn't lie to them, we used a simpler model that just no longer is accurate enough for our purposes.
Where does the College Board come down on the definition of what mass actually measures?
Anonymous, your distinction is correct but, as you note, a step deeper in complexity than is appropriate for first-year physics. I'd suggest that this distinction is unimportant even in AP1 or APC. Any time we can simplify without losing predictive power, we should do so. If they become a practicing chemist or physicist, they'll learn the difference and say "oh, that makes so much sense."
ReplyDeleteAs for the CB and the AP exams... the AP1 exam does distinguish between gravitational mass and inertial mass, though it doesn't worry about moles and the "amount of substance." And that distinction is only important on a very few specifically targeted questions. A student will not get into trouble by saying on a FRQ "this object is still the exact same object, so hasn't gained or lost stuff, so still has mass 100 kg."