A jet airplance travelling at the speed of ` 500 km ^(-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 burnt gases with respect to observer on the ground ?

Options

A. `-100 kmph`
B. `-1000 kmph`
C. `-10 kmph`
D. `-11 kmph`

Answer

B

Explanation

Velocity of jet aeroplane `= 500 hat(j)`
Velocity of fuel w.r.t. plane `= - 1500 hat(j)`
`:. Vec(v)_(f) - vec(v)_(p) = - 1500 hat(j), vec(v)_(f) = vec(v)_(p) - 1500 hat(j)`
`= 500 hat(j) - 1500 hat(j) = - 1000 hat(j)`
`:.` Speed of fuel w.r.t. ground is `-1000 km//hr`.
So, `n xx 5 = (1)/(2) xx 10 xx (1)^(2) " or " n = 1`