**Question:**

**Ten small planners are flying at a speed of 150 km/h in total darkness in an air space that is 20 × 20 × 1.5 km3 in volume. You are in one of the planes, flying at **

**random within this space with no way of knowing where the other planes are. On the average about how long a time will elapse between near collision with your **

**plane. Assume for this rough computation that a safety region around the plane can be approximated by a sphere of radius 10 m.**

**Solution:**

Time = distance/speed

No.of particles per unit volume v = N/volume

n = 0.0167 km-3

d = 10 × 10-3 km

v = 150 km/hr

Therefore, time = 225 hrs