A small object at rest absorbs a light pulse of power 20 mW and duration 300 ns. Assuming speed of light as 3 × 10⁸ m s⁻¹, the momentum of the object becomes equal to:
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A small object at rest absorbs a light pulse of power 20 mW and duration 300 ns. Assuming speed of light as 3 × 10⁸ m s⁻¹, the momentum of the object becomes equal to:

G1 Physics · Accepted Answer

Energy absorbed E = Pt = (20×10⁻³)(300×10⁻⁹) = 6×10⁻⁹ J. Photon momentum transferred p = E/c = 6×10⁻⁹/(3×10⁸) = 2×10⁻¹⁷ kg m s⁻¹.