a car is moving at a constant speed along a straight line. which statement is true about the forces acting on the car?
a.
the net force acting on the car from all directions is zero.
b.
the net force acting on the car is greater than the car's weight.
c.
the net force acting on the car is in the direction of the car's motion.
d.
the net force acting on the car is in the opposite direction of the car's motion.

A. The net force acting on the car from all directions is zero.

Explanation:

According to Newton's first law of motion, an object continues its uniform motion along a straight line, the net force acting on the object will be zero.

To experience a force, the object needs to change its speed or the direction of motion. Unless it experiences any change in the magnitude of speed or direction. The car doesn't experience any force.

If car is moving with a uniform speed in a circular motion. The net force acting on the car is not equal to zero. Since the car is changing its direction constantly, a force called centripetal force is acting on it.

Hence, if the car moves in a straight line, the net force acting on the car from all directions is zero.

A.  The net force acting on the car from all directions is zero.

Explanation:

By Newton's first law, an object stays at rest if initially at rest and and keeps moving with same velocity if initially at motion unless an external force is applied.

By Newton's second law, the acceleration of a body is directly dependent on the force applied to the object.

Form the above stated laws of Newton, we can conclude that

1) Any body which is moving with a constant velocity continues to do so unless an external force is acted on it.

2) If a body is moving at constant velocity, then its acceleration is =0 and thus the net force is=0 as it is dependent on force applied.

∴ The net force acting on the car from all directions is zero.

you would expect a sound wave to speed up. - b)