Problem 8 on Motion in a Straight Line

Description:

Problem

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

Solution

Assume the jet plane is travelling East. Hence, the sign convention we choose is −

• East as positive direction.
• West as negative direction.

Velocity of jet plane with respect to ground, v_J = 500 km/h

Velocity of exhaust with respect to jet plane, v_EJ = −1500 km/h

Using the equation of relative velocity,

v_EJ = v_E - v_J

-1500 = v_E - (500)

v_E = -1000 km/h

Hence, Speed of Exhaust w.r.t. ground = 1000 km/h