Measurement and Estimation
page 3
MEASUREMENT and ESTIMATION
1.
Try this one. The equator of the planet Mercury is about two-fifths as long as the
equator of the Earth. The density of Mercury is not very different from the density
of Earth. The “rotational moment of inertia” of planet Earth turns out to be about
9  1037 kg m2. What is the rotational moment of inertia of Mercury?
2.
The SI unit of power is the watt.
kg m 2
1 watt  1 W  1 3
s
A certain car company advertises that their new two ton car can go from “0 to 65
in 5.9 seconds” (which is basically from rest to a speed of 30 m/s in six seconds).
What is the minimum amount of power that the engine must be able to produce to
achieve this? (Answer in watts, but car companies think in terms of horsepower,
where 1 horsepower is about 750 watts).
3.
Look at a penny, a marble, or a fingernail. The moon is about 400,000 km away.
Roughly what is the diameter of the moon?
4.
A certain silicon computer microchip is composed of individual elements that are
roughly cubic in shape, 32 nm on a side (1 nm = 10-9 m). The density of silicon is
about 2.3 grams per cubic centimeter, and one mole of silicon (6 x 1023 atoms) has
a mass of 28 grams. Engineers squeeze 1 billion (109) transistors into one of these
computer chips. If each element is a cube which is 32 nm on a side, how many
atoms are there along an edge of the cube?