Question

A jet aeroplane travelling at the speed of 500 km h^–1 ejects its products of combustion at the speed of 1500 km h^–1 relative to the jet plane. What is the speed of the latter with respect to an observer on ground?

Answer 1

Speed of the jet airplane, v_jet = 500 km/h
Relative speed of its products of combustion with respect to the plane,
v_smoke = – 1500 km/h
Speed of its products of combustion with respect to the ground = v′_smoke
Relative speed of its products of combustion with respect to the airplane,

The negative sign indicates that the direction of its products of combustion is opposite to the direction of motion of the jet airplane.