Question

A toy plane weighing 1.5 kg is flying in the air at 8 m/s. The player
turns down its speed to 6m/s. What is the work done on it?

Answer 1

Use the work-energy theorem. The total work done on the plane is equal to the change in its kinetic energy:

W = ∆K

W =  1/2 (1.5 kg) (6 m/s)² - 1/2 (1.6 kg) (8 m/s)²

W = -21 J

(Note that the work must be negative since the "braking" force opposes the direction in which the plane is moving.)