A car is driven on a flat road. The force of the engine is constantly opposed by the force of air resistance, which depends on the speed of the vehicle. Consider four cases:
The engine force is equal to the resistance force. The magnitude of each is 0 N.
The engine force is 800 N and the resistance force is 200 N.
The engine force is equal to the resistance force. The magnitude of each is 400 N.
The engine force is 200 N and the resistance force is 400 N.
Which of the cases does Newton's first law describe?
