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.
Answer (1)
The car moves at a constant speed along a straight line.
Newton's first law implies that the net force must be zero for constant motion.
Newton's second law ( F = ma ) confirms that zero acceleration means zero net force.
Therefore, the net force acting on the car is 0 .
Explanation
Understanding the Problem We are given that a car is moving at a constant speed along a straight line. We need to determine which statement is true about the forces acting on the car.
Applying Newton's First Law Newton's first law of motion states that an object in motion stays in motion with the same speed and in the same direction unless acted upon by a net force. This means that if the car is moving at a constant speed in a straight line, the net force acting on it must be zero.
Applying Newton's Second Law Newton's second law of motion states that F = ma , where F is the net force, m is the mass, and a is the acceleration. Since the car is moving at a constant speed, its acceleration is zero. Therefore, the net force acting on the car is F = m × 0 = 0 .
Conclusion Therefore, the net force acting on the car from all directions is zero.
Examples
Consider a cyclist riding at a constant speed on a flat, straight road. The force the cyclist applies to the pedals to move forward is balanced by the opposing forces of air resistance and friction from the road. If these forces are perfectly balanced, the net force is zero, and the cyclist maintains a constant speed. This principle applies to various scenarios, from vehicles to even objects in space, illustrating how balanced forces result in constant motion.
