An aeroplane is observed by two persons travelling at 60 km h⁻¹ in opposite directions along a straight road. To one observer the plane appears to cross the road at right angles; to the other it appears at 45°. At what angle θ does the plane actually cross the road?

Question

G1 Physics · Accepted Answer

Let road be x-axis. For one observer, apparent motion perpendicular to road gives plane x-component=60. For the observer moving opposite, relative x-component=120 and apparent angle45°, so plane y-component=120. Thus tanθ=120/60=2. Option B.