An amateur race car driver buys a used Datsun car for drag racing. It
can attain highway speed with an
acceleration of 3.76 m/s^2. By making
changes to its engine, he can
increase the net horizontal force on
the car by 24.0%. With much less
expense, he can remove material
from the body of the car to decrease
its mass by 24.0%. (a) Which of these
two changes, if either, will result in
the greater increase in the car's
acceleration? (b) If he makes both
changes, what acceleration can she
attain?

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speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.

snell's law

refractve index = sin incidence / sin refraction