A small spaceship with a mass of only 2.6 ✕ 103 kg (including an astronaut) is drifting in outer space with negligible gravitati
onal forces acting on it. If the astronaut turns on a 12 kW laser beam, what speed will the ship attain in 1.0 day because of the momentum carried away by the beam?
To work this problem we must use the relationship between the amount of movement and energy for an electromagnetic wave
p = U / c
They give us the power of the laser, which is the relationship between work and time. Work is the variation of energy, in a laser beam that is an electromagnetic wave. We have its power
P = W / t
W = P t
Work is the variation of energy W = U
p = P t / c
½ m v = P t / c
v = 2 P t / m c
Let's reduce time to SI units
t = 1.0 day (24 h / 1 day) (3600 s / 1 h) = 86400 s
It is common for domestic electrical installations to use copper wire with a diameter of 2.05 mm. Determine the resistance of such a wire with a length of 24.0 m.
