Round-trip time for light using speed of light formula

Steps:

• Calculate total distance: 2 × 150 m = 300 m (to wall and back).
• Use speed of light: c = 3 × 10^8 m/s.
• Compute time: t = distance / c = 300 / (3 × 10^8) = 1 × 10^{-6} s.
• Convert to microseconds: 1 × 10^{-6} s = 1 μs.

Why D is correct:

• Matches formula t = 2d / c, where d = 150 m and c = 3 × 10^8 m/s, yielding exactly 1 μs.

Why the others are wrong:

• A: 0.5 ns is 5 × 10^{-10} s, far too small for 300 m at light speed.
• B: 0.1 ns is 1 × 10^{-10} s, even smaller and ignores round-trip distance.
• C: 0.5 μs is time for one-way trip (150 m), not round trip.

Final answer: D