Question

A jet air plane traveling at a speed of $500\text{km/hr}$ ejects its products of combustion at the speed of $1500\text{km/hr}$ relative to jet plane. What is the speed of combustion products w.r.t an observer on the ground?

• A. $1000\text{km/hr}$
• B. $500\text{km/hr}$
• C. $2000\text{km/hr}$
• D. $5000\text{km/hr}$

Answer 1

The correct option is A $1000\text{km/hr}$

Speed of the jet airplane with respect to ground is, $V_{\text{jet,g}}=500\text{km/h}$ .
Relative speed of its products of combustion with respect to the plane.
$V_{\text{smoke,jet}}=-1500\text{km/h}$
Speed of its products of combustion with respect to the ground $=V_{\text{smoke, grd}}$
Relative speed of its products of combustion with respect to the airplane,
$V_{\text{smoke, grd}}=V_{\text{smoke,jet}}+V_{\text{jet, grd}}$
$V_{\text{smoke, grd}}=-1500+500$
$V_{\text{smoke}}=-1000\text{km/h}$