The force diagram shows an aircraft accelerating. At the instant shown, the velocity of the aircraft is 40 m s-1.

Question 31

The force diagram shows an aircraft accelerating. At the instant shown, the velocity of the aircraft is 40 m s^-1.

At which rate is its kinetic energy increasing?

A 2.4 MW                    B 8.0 MW                    C 12 MW                     D 20 MW

Reference: Past Exam Paper – March 2016 Paper 12 Q15

Solution:

Answer: C.

The ‘rate of increase of kinetic energy’ has unit J/s. This is the unit for power.

The forward acceleration is due to a resultant force horizontally.

Horizontally, resultant force = engine thrust – air resistance

Resultant force = 500 – 200 = 300 kN

Power = Force × velocity

Power = 300 000 × 40 = 12 000 000 W

Power = 12 MW