Question

An airplane travels 2100 km at a speed of 800 km/hr, and then encounters a tailwind that boosts its speed to 1000 km/hr for the next 1800 km. What was the average speed of the plane for this trip?

Answer 1

`v=(d)/(t)\to d=vt\to t=(d)/(v)\\\\d_1=2100km;\ v_1=800km/h\\\\t_1=(2100)/(800)h=(21)/(8)h\\\\d_2=1800km;\ v_2=1000km/h\\\\t_2=(1800)/(1000)h=(18)/(10)h\\\\The\ average\ speed:v=(d_1+d_2)/(t_1+t_2)\\\\d_1+d_2=2100km+1800km=3900km\\\\t_1+t_2=(21)/(8)h+(18)/(10)h=(21\cdot5)/(8\cdot5)h+(18\cdot4)/(10\cdot4)h=(105)/(40)h+(72)/(40)h=(177)/(40)h\\\\v=(3900)/((177)/(40))km/h=3900\cdot(40)/(177)km/h\approx\boxed{881\ km/h}`

Answer 2

If an airplane travels 2100 km at a speed of 800 kn/hr and then encounters a tailwind that will boost the speed to 1000 km/hr for the next 1800 km. The average speed of the plane for this particular trip was 881.36 km/hr.