Question

What is the travel time for a laser pulse to reach an object with an elevation of 210m, when the flying height is 510m?

• A. \(\text{2000 second} \)
• B. \(\text{2000 millisecond} \)
• C. \(\text{2000 microsecond} \)
• D. \(\text{2000 nanosecond} \)

Hint:

Laser pulses travel at the speed of light (\( 3 \times 10^8 \) m/s), and the total distance is twice the flying height minus ground elevation.

Answer 1

The Correct Option is D

Step 1: Understanding laser pulse travel time. The travel time (\( t \)) of a laser pulse is given by: \[ t = \frac{2d} {c}  \] where: - \( d \) is the round-trip distance, - \( c \) is the speed of light (\( 3 \times 10^8 \) m/s), - The object elevation is 210m, and the flying height is 510m, so the downward distance is: \[ d = 510 - 210 = 300m. \] 
Step 2: Calculating total travel time. Since the laser pulse travels to the object and back: 
 \(\text{Total distance} \) = \(2 \times\)300 = 600m. 
 \( t = \frac{600} {3 \times 10^8} \) 

\( t = 2 \times 10^{-6}\)
 \(\text{ seconds} \) = 2000 \(\text{ nanoseconds} \).  
Step 3: Selecting the correct option. Since the computed travel time is 2000 nanoseconds, the correct answer is d. 2000 nanosecond.