The Japanese government has recently purchased a laser with power P = 1.0MW = 1

Question

The Japanese government has recently purchased a laser with power P = 1.0MW = 1 × 106W to cut up the debris from the Fukushima nuclear power plant disaster. This laser will allow the contaminated concrete and steel to be cut from one mile away. Unfortunately, the laser costs 3 billion dollars, so we can’t get one. This laser can also be used to accelerate satalites into orbit. If the laser shines on a perfectly reflecting gold mirror attached to the satellite and the laser beam is circular with a 1.5cm radius, how much force does it the laser light exert on the mirror?

Note, to use this laser to launch a satellite, you don’t use the radiation pressure. You attach some padding to the satellite and vaporize the padding. The vaporized padding forms the rocket exhaust.

(a) 1.1 × 107N (b) 2.1 × 105N (c) 3.3 × 103N (d) 6.7 × 103N (e) 1.4 × 101N

(f) Toby

Explanation / Answer

For a perfectecly reflecting surface,the radiation pressure on it is p = 2I / c

where I is the intensity of laser and I = P / A

P is power of laser beam and A is area of it.

Thus p = 2P / ( A * c )

The force exerted by the laser light on the mirror is

F = p *A = 2P / c = 2 * 106 / (3 * 108 ) = 6.667 *10-3 N

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