Question

An echo is heard by a radar in 0.08 s. If the velocity of radio waves is 3 × 10⁸ ms⁻¹, the enemy plane is at a distance of:

Options

• 120 km

• 120000 km

• 12000 km

• 1200 km

Answer 1

12000 km

Explanation:

The radio waves travel to the plane and back, so the distance to the plane is half the total distance travelled.

$$d = \frac{vt}{2}$$

$$ = \frac{3 \times 10^{8} \times 0.08}{2}$$

= 1.2 × 10⁷ m

= 12000 km