PHYSICS
 

Platte Canyon High School
Bailey, Colorado

Student Stuff 

STUDENT STUFF
Problems of the Week

September 17, 2001

The Bikes and the Bee

Two bicyclists travel at a uniform speed of 10 m/s toward each other.  At the moment when they are 20 km apart, a bumble bee flies from the front wheel of one of the bikes at a uniform speed of 25 m/s directly to the wheel of the other bike.  It touches it and turns around in a negligibly short time and returns at the same speed to the first bike, whereupon it touches the wheel and instantaneously turns around and repeats the back-and-forth trip over and over again – successive trips becoming shorter and shorter until the bikes collide and squash the unfortunate bee between the front wheels.  What was the total mileage of the bee in its many back-and-forth trips from the time the bikes were 20 km apart until its hapless end?

September 24, 2001

Speed Ain’t Acceleration

As the ball rolls down this hill, what happens to its speed and acceleration (increase, decrease, remain constant)?

October 1, 2001

Two Bubbles

If all space were empty except for two nearby masses say two drops of water, the drops would, according to Newton’s Law of Gravity, be attracted together.  Now suppose all space were full of water except for two bubbles.  How would the bubbles move?

October 8, 2001

Strongman

When the strongman suspends the 10-N telephone book with the rope held vertically the tension in each strand of the rope is 5 N.  If the strongman could suspend the book from the strands pulled horizontally as shown, what would be the tension in each strand?

October 15, 2001

Jar of Flies

A bunch of flies are in a capped jar.  You place the jar on a scale.  The scale will register the most weight when the flies are (a) sitting on the bottom of the jar, (b) flying around inside the jar, or (c) the weight of the jar is the same in both cases.

October 22, 2001

Poof and Foop

If a can of compressed air is punctured and the escaping air blows to the right, the can will move to the left in a rocket-like fashion.  Now consider a vacuum can that is punctured.  The air blows in the left as it enters the can.  As the vacuum is filled, how will the can be moving?

October 29, 2001

Ball on a String

A ball held by a string is coasting around in a large horizontal circle.  The string is then pulled in so the ball coasts in a smaller circle.  Will the ball be coasting at a greater, lesser or the same speed in the smaller circle compared to the larger circle?

November 5, 2001

Rolling in the Rain

Suppose an open railroad car is rolling without friction in a vertically-falling downpour and an appreciable amount of rain falls into the car and accumulates there.  Consider the effect of the accumulating rain on the speed, momentum and kinetic energy of the car.

November 12, 2001

Quicksilver Sea

Suppose the water in the ocean turned into quicksilver (which is about 13 times as dense as seawater).  Then compared to the speed of seawater waves, the quicksilver waves would move faster, slower or at the same speed.

If the strength of the earth’s gravity increased, ocean waves would move faster, slow, neither faster nor slower.

November 19, 2001

Sound Barrier

Two bullets are moving through air.  From the bow waves produced by the bullets, we can say for sure that

a.  both bullets must be traveling faster than the speed of sound waves and Bullet I is moving faster than Bullet II.

b.  Bullet I is moving faster than Bullet II, but not necessarily faster than the speed of sound

c.  none of the above.

November 26, 2001

Plane Mirror

What must be the minimum length of a plane mirror in order for you to see a full view of yourself?

December 3, 2001

A magnifying glass in the sink

If a magnifying glass is held under water its magnifying power is increased, decrease, or same as it was out of water.

December 10, 2001

Bubble Lens

Underwater is a bubble.  A light beam shines through it.  After passing through the bubble the light beam converges, diverges, or is unaffected.

December 17, 2001

Under the Influence

Two uncharged metal balls, X and Y, stand on glass rods.  A third ball, Z, carrying a positive charge, is brought near the first two.  A conducting wire is then run between X and Y.  The wire is then removed, and ball Z is finally removed.  When this is all done it is found that

a.     balls X and Y are still uncharged

b.    balls X and Y are both charged positively

c.     balls X and Y are both charged negatively

d.  ball X is + and ball Y is –ball X is – and ball Y is +

January 2, 2002

Jar of Electricity

A Leyden Jar is an old-fashioned capacitor.  Now a capacitor, or condenser, as they are sometimes called, consists of metal surfaces that are separated from one another.  They are storehouses of electric energy when one surface is charged + and the other surface -.  Two hundred years ago capacitors were made by putting one piece of metal foil on the inside of a bottle and one piece on the outside.  The bottle was called a Leyden Jar because the first were made at the University of Leyden in Holland – the Cal Tech of its day.  The energy stored in a charged Leyden Jar is actually stored

a.     on the metal foil inside the jar

b.  on the metal foil outside the jar

c.   in the glass between the inner and outer foil

d.   inside the jar itself.

January 7, 2001

High Voltage Bird Again

Suppose a bird stands with its legs bridging the light bulb in the circuit shown.  Describe what will happen to each of the birds if the switch is closed.

January 7, 2001

The Magnetic Rats Nest

The sketch above shows a long wire running from A to B which has been tangled into a “rats nest”.  It also shows a short straight segment of wire CD.  Now imagine an electric current flowing from A to B and another one flowing from C to D (you must have batteries, or something, in your imagination).  Because of the current, a certain force is exerted on wire CD.  Now in your imagination reverse all the electric currents so that the reversed current now flows form B to A and from D to C.  The force on the short, straight segment of wire will be reversed, be as it was, vanish, perpendicular to the way it was, or be in a direction not mentioned above.

January 7, 2001

Light Clock (Again)

A rocket ship that emits flashes of light every 6 minutes travels between two planets, A and B.  It travels away from A and toward B.  If its flashes are seen at 3 minute intervals on B, then on planet A, the flashes are seen at what interval?