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- Radioactive Decay [10/26/2004]
The half-life of a radioactive element is 131 days, but your sample
will not be useful to you after 90% of the radioactive nuclei
originally present have disintegrated. For about how many days can you
use the sample?
- Radioactive Decay of an Isotope [01/05/1998]
I know the decay of the 226Ra isotope involves the use of logarithms (an
exponential function ae^x), but I'm having trouble fitting my information
to my equation...
- Radius of a Racing Circle [09/20/1999]
How can I find the equation for the radius of a 'racing circle' (the
fastest path a racecar can take through the corner defined by the
quadrants of two circles), an arc sandwiched between identical quadrants
of two concentric circles?
- Rainfall on a Moving Object [09/10/2002]
I would like to figure out the relation between a moving object (a
person) and the amount of rain that will hit him given a fixed
- Rain - Run or Walk? [08/05/2003]
Is there an optimum speed at which to walk through the rain to
minimise the number of drops you get hit by?
- Range of the Coefficient of Friction [10/18/2000]
Can the coefficient of friction be greater than one?
- Rate of acceleration/gravity [04/09/1997]
If a ball is dropped from a building and hits the ground after 3 seconds,
how tall is the building?
- Rate of Change of Distance [05/02/2002]
Speed is defined as the rate of change of distance moved with time.
What is meant by 'rate of change of distance'?
- Rate of Flow Through a Pipe [06/30/1999]
How much fluid would be dispensed after 1 hour from a line 3/8" in
diameter at a pressure of 150 psi?
- Relative Density [05/18/2000]
A solid object floats in water with three-fourths of its volume beneath
the surface. What is the object's density?
- Relative speed [11/30/1994]
Two vehicles are travelling at 60 mph. One is a 50-foot flatbed truck
with a drive-on ramp lowered down to the roadway. The second is a rear
wheel drive sedan only 3 feet directly behind the flatbed truck. It is
capable of coming to a complete stop from 60 mph in 120 feet. The truck
slows to 59 1/2 mph. Since the car is gaining on the truck at a rate of
1/2 mph, the front wheels of the car begin to slowly move up the ramp.
Question: When the rear tires finally make direct contact with the ramp,
will the car, which was moments ago traveling at 1/2 mph relative to the
truck's ramp, suddenly go from 1/2 mph ramp speed to 60 mph ramp speed
and thus crash into the back of the truck's cab section?
- Relativity [05/22/2002]
How do you demonstrate algebraically that [the following expressions]
are proportional to each other even when they describe 'events' that
are not on the expanding wavefront of light?
- Relativity and Quantum Theory [03/15/2002]
What is the problem between relativity and quantum theory that scientists
are trying to solve?
- Resistance Across Cubic Network [12/18/2003]
Given a cube with resistors at each corner, how can I find the
resistance between any pair of corners?
- Rock Falling From Building [9/12/1996]
A rock is dropped from a tall building and hits the ground at 224 ft/
sec. How long did it take for the object to fall?
- Rotational Symmetry [11/05/1997]
I am looking for a precise definition of rotational symmetry of a figure
in a two-dimensional plane.
- Rotation of Rigid Bodies [02/05/1999]
Rotation of rigid bodies, and the kinetic and potential energies
- Safe Passing Distance [07/30/1999]
If a car traveling 55 mph passes a car traveling 50 mph, what distance
does the faster car travel to get around the slower car?
- Savings on Gasoline [05/22/2001]
Your old car averaged 22 mpg and you new car should average 37 mpg.
Suppose you drive 12,500 miles per year and the cost of gas averages
$1.85 per gallon. How much will you save on gasoline each year?
- The Schroedinger Wave Equation [09/10/1998]
Can you help me understand the concepts behind Schroedinger's wave
- Series and Parallel Circuits [10/18/2000]
Can you show me how to calculate voltage, current, resistance, and power
in a series-parallel circuit?
- Sextant Theorem [05/13/2001]
What mathematical theorem is behind using a sextant, and can it be
- Ships and Sea Level [03/23/2002]
How would removing all ships from the ocean affect sea level?
- Ships in the Fog [02/01/1999]
Given the locations and speeds of two ships, find whether (and when) they
- Shot Out of a Cannon [10/12/1998]
A performer is shot out of a cannon at 30 degrees from the horizontal, to
land 20 meters away... What should his initial speed be?
- Significance of e = mc^2 [7/26/1996]
What does e = mc^2 mean?
- Significant Figures and Scientific Notation [05/21/1997]
How do you tell how many significant figures a number has?
- Simulating Sound Waves [10/27/2000]
How can I simulate a sound wave that reaches a maximum height every
- Size of the Universe [10/31/2001]
Is it possible to measure the size of the universe?
- Solving a Decibel Noise Equation [05/23/2000]
How do you rearrange the formula 50 = 94.5 - 20log(r) - 8 to solve for r?
- Space Shuttle Debris [06/24/2003]
Why are they shooting debris at the wing at 550 mph to assess damage?
- Special Relativity and Temperature [12/21/2005]
If temperature is the total amount of kinetic energy possessed by the
particles in a given substance, and special relativity holds that
nothing can move faster than the speed of light, does that mean that
there is an upper limit for how hot a substance can become (e.g. the
temperature where the particles begin to move at the speed of light)?
- Specific Gravities in Large Volumes [04/09/2002]
I am trying to create a chart that could be used to help determine
what weight of methanol/water to use to either raise or lower the
specific gravity of a volume of corrosion inhibitor in bulk mixing
- Speed down a Hill [4/17/1996]
How fast is an object going at the bottom of a 14.9m hill, if it starts
at the top going 3.0 m/s?
- Speed of a Rotating Disc [03/01/1998]
The outer edge of a CD travels farther than the inner edge - does the
outer edge spin faster?
- Speed of Atoms [02/25/2002]
What is the speed of the atoms or molecular activity of something as hot
as the sun? Will this not be faster than the speed of light?
- Speed of Light [06/08/2001]
What's m s^-1? Why isn't it just m/s (meters per second) instead? What's
the little "-1" at the end?
- Speed of Peeling Potatoes with Different Surface Areas [09/11/2006]
Joe and Harry have been assigned the task of peeling potatoes. Joe is
given 40 kg of potatoes, which average 1 kg in size, while Harry is
given 20 kg of potatoes, which average 0.5 kg in size. Assuming that
Joe's and Harry's peeling skills are equal, and if Joe finishes his
task in one hour, how long will it take Harry to accomplish his task
- Speed of Sound in a Rod [07/05/1999]
How long is an iron rod if a sound originating at one end is heard in the
rod 1 second before it is heard in the air?
- Stopping Distance [02/25/1997]
A car is traveling at 25m/s. The brakes are suddenly applied; how far
will the car slide once the brakes are applied?