Question

a jet airplane travelling at the speed of 500 km/h ejects the burnt gases at a speed of 1200km/h relative to the jet airplane. find the speed of the burnt gases w. r. t the observer on earth.

Answer 1

Jet speed=500

Gas speed relative to jet=1200

Since jet and gas flows in opposite direction the speed of jet w.r.t observer is

1200-500=700 kmph

Answer 2

Answer:

Speed of the jet airplane, vjet = 500 km/h

Relative speed of its products of combustion with respect to the plane,

vsmoke = – 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,

vsmoke = v′smoke – vjet

– 1500 = v′smoke – 500

v′smoke = – 1000 km/h

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