If a motorcycle moves with a constant velocity, can you conclude that there is no net force acting on it?

 Yes

Explanation:
Newton's Law of motion is
F = ma
where F = force,
m =mass,
a = acceleration.

Because the motorcycle moves with a constant velocity, the acceleration is zero, and there is no net force.

Although there is no net force, there are many forces that are in equilibrium.
(i) There is the driving force that is provided by the engine,
(ii) There is wind resistance,
(ii) There is frictional resistance.

At constant velocity, the sum of resistive forces is equal to the driving force.

The anwser is: wave a has a greater pitch and frequency.