23.72.
Set Up:
Find the force on her due to the momentum carried off by the light. Express this force in terms of
the radiated power of the flashlight. Find the acceleration produced by this force.
Solve: (a)
The radiation pressure is
Force is (pressure)
A
, so
were
P
is the power output of the
flashlight. The acceleration produced by this force is
gives
(b)
She could throw the flashlight in the direction away from the ship. By conservation of linear momentum she
would travel toward the ship with the same magnitude of momentum as she gave the flashlight.
23.73.
Set Up:
For a totally reflective surface the radiation pressure is
Find the force due to this pressure and
express the force in terms of the power output
P
of the sun. The gravitational force of the sun is
Solve: (a)
The sail should be reflective, to produce the maximum radiation pressure.
(b)
where
A
is the area of the sail.
where
r
is the distance of the sail from the sun.
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 Spring '07
 Shoberg
 Acceleration, Force, Momentum, Power, Light

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