Q#31 (Past Exam Paper – March 2016 Paper 12 Q15)
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
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
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