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Quiz_3_sol - Solution F = dpd t = dUd t c where dUd t = 1.0...

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Problem 1 (5 points) What is the radiation pressure exerted on a light-absorbing surface by a laser beam whose intensity is 180 W/cm 2 . Solution: Pa c S dt dU Ac A F P 3 10 6 1 - × = = = = Problem 2 (5 points) The average intensity of noonday sunlight is about 1 kW/m 2 . What is the radiation force on a solar collector measuring 60 cm by 2.5 m if it is oriented at right angles to the incident light and absorbs all the light? Solution: F = PA , c S P = N c A S F 6 8 3 10 5 ) 10 3 ( 10 ) 5 . 2 6 . 0 ( - × = × × × = = Problem 3 (10 points) A 65-kg astronaut is floating in empty space. If the astronaut shines a 1.0-W flashlight in a fixed direction, how long will it take the astronaut to accelerate to a speed of 10 m/s?
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Unformatted text preview: Solution: F = dpd t = ( dUd t ) c , where dUd t = 1 .0 W . v = at ⇒ t = va = mvF ⇒ ⇒ t = (65 kg )(10 ms )(3 × 10 8 ms )(1 W ) = 1 .95 × 10 11 s ≈ 6 × 10 3 y Problem 4 (10 points) A laser beam shines vertically upward. What laser power is necessary for this beam to support a flat piece of aluminum foil with mass 30 mg and diameter equal to that of the beam? Assume that the foil reflects all the light. Solution: N mg F foil 4 6 10 94 . 2 ) 8 . 9 )( 10 30 (--× = × = = ; dt dU c F rad 1 2 = dU d t = (12 ) F fo il c = (12 )(2 .94 × 10-4 N )(3 × 10 8 ms ) = 4 .26 × 10 4 W...
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