Suppose such a sail is constructed of a highly reflective material thin enough s

Question

Suppose such a sail is constructed of a highly reflective material thin enough so that one square meter of the sail has a mass of just 3 x 10-3 kg. The sail is to be propelled by an ultraviolet laser beam (wavelength = 225 nm) that will strike its surface perpendicularly. Use the impulse-momentum theorem to determine the number of photons per second that must strike each square meter of the sail in order to cause an acceleration of 9.8 x 10-6 m/s2, which is one million times smaller than the gravitational acceleration at earth's surface. Assume that no other forces act on the sail, and that all the incident photons are reflected?

Explanation / Answer

a)momentum change per photon=2h/

reqd force=ma=7.448*10^-8 N

so no of photons/sec=force/mom change=1.07*10^19

b)power = energy of a photon * no of photons/sec=11.07 watts/m^2

:)

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