LSMSA Science Question

Be the first to submit the sufficiently correct answer to Robert to win your choice of either 1) the book "Physics in the 20th century" or 2) an intermittenly working DVD recorder that is ready for disassembly or 3) a 4-gigabyte micro SD card.

November 2008: Three billiard balls have equal mass m and velocity v. Mathematically describe a situation in which the three come to a complete stop due to a mutual collision. For 4 masses of 1 kg, 2 kg, 3 kg, and 4 kg moving at speeds 1 m/s, 2 m/s, 3 m/s, and 4 m/s, find four angles such that the vector sum of the four momentums is zero. In this situation, a mutual collision among the four particles would cause all of them to stop.

October 2008: How many homes are there in Louisiana? How much power does the average home use each year? What portion of this energy is used to heat water? How much energy, in megawatt-years, is used every year to heat water in Louisiana homes?

September 2008: A cart slides down an inclined plane having coefficient of friction µk. When the cart has speed vc, a ball is launched from the cart at speed vP in a direction perpendicular to the inclined plane. The cart continues moving down the plane. When the ball lands back on the inclined plane, how far will it be from the cart? If there were no friction, would the ball land back on the cart?

Aug 2008: How many strands of beads are thrown during a typical Mardi Gras parade in New Orleans? What is the number of parades needed for the thrown beads to stack from New Orleans to the moon?

September 2007: KW Daily determined the infinite sum that represents the distance that a bouncing ball travels. The question was: A steel bearing is dropped from a height h above a steel plate that is on the ground. The bearing rebounds to a height of 0.9 h and then falls again. It repeats this rise and fall motion, each time rebounding to 90% of the height reached on the previous bounce, until it comes to a stop. What will be the total distance traveled by the bearing before it comes to rest on the plate at the ground?

August 2007: KW Daily correctly answered that "jerk" is the name given to the rate of change of acceleration. This is an appropriate name when, for example, riding in a car that repeatedly increases and decreases its speed every five seconds, repeatedly throwing you forward and backward in a jerking and uncomfortable motion.

April 2007: One can see right through water that is sitting in a glass. Water is clear, but when you spill water on your shirt, the wet area becomes dark? Doesn't that mean the glass of water should be dark, not clear? The question is, when you spill water on your shirt why does the shirt then appear darker? Riley Adams correctly answered that the shirt itself has little mass. Light from the sun bounces off the shirt after encountering a single reflection. The shirt has much more mass when the water is added. Sunlight now hits the sirt and then bounces off several water molecules, becoming dimmer with each reflection, which is absorption followed by emmission. The spot on your shirt appears less bright because of the multiple reflections that occurred before the light ended up in your eye.

March 2007:
When you drive down the highway at the posted speed limit, why doesn't the dust blow off of your car. Why doesn't the dust blow off the fan used to cool a room in your house? Fans are always full of dust. Marcus Toussaint correctly answered that "the layer of air next to the fan blade is stationary--relative to the fan." A thin boundary layer occurs in which the speed of the flow becomes zero as the flow nears the surface. The dust does not blow off because the air is not moving in the last fraction of a millimeter nearest the surface. That non-moving air is stuck to surface as peanut butter would do. When you put peanut butter on a knife and then spread a thick layer onto bread, the peanut butter is not moving at the surface of the bread. A little ways outward from the bread, the peanut butter will be moving at half the speed of the knife, and a little further outward, the peanut butter is moving at the speed of the knife. A fluid has a “viscous boundary layer” in which both the tangential and normal flow speeds become zero. Certain small creatures live within the boundary layer where the wind doesn’t blow or the water doesn’t move. (The results of theoretical fluid mechanics did not match reality very well until this boundary condition was deduced. Is there a still-unknown boundary condition at the transistion between macro and molecular systems?)

February, 2007 Question:
All materials consist of atoms and molecules that are mostly empty space. Water, glass, and wood consist of such atoms and molecules, but we can see through glass and water but not wood. Why? Andrew Moore corectly explained that the energy levels of the individual atoms in glass are not such that they absorb light in the visible spectrum, although they will absorb infrared and ultraviolet light. This makes them visibly transparent. The transparent material absorbs no colors that we can see with our eyes.