Question

If the plane maintains a constant speed and altitude and travels in a straight line, which of the following must be true according to Newton's law of inertia? (A) The plane is weightless. (B) There are no unbalanced forces acting on the plane. (C) The lift must be greater than the weight to keep the plane from falling to the ground. (D) The thrust must be greater than the drag to keep the plane moving forward.

Short answer

(B) There are no unbalanced forces acting on the plane.

Step-by-step solution

Evaluate statement A

Statement A says that the plane is weightless. A plane can never be weightless unless it's outside the gravitational field of the earth or in a state of free-fall. So, statement A is not true according to Newton's law of inertia.

Evaluate statement B

Statement B says that there are no unbalanced forces acting on the plane. According to Newton's first law, an object moving at a constant velocity (which includes constant speed and direction) will continue to move at that constant velocity unless acted upon by an unbalanced force. Since the plane is maintaining a constant speed, altitude, and is traveling in a straight line, there are no unbalanced forces acting on the plane. So, statement B is true according to Newton's law of inertia.

Evaluate statement C

Statement C says that the lift must be greater than the weight to keep the plane from falling to the ground. In fact, for the plane to maintain a constant altitude, the lift must be equal to the weight of the plane, not greater than it. Thus, statement C is not true according to Newton's law of inertia.

Evaluate statement D

Statement D says that the thrust must be greater than the drag to keep the plane moving forward. To maintain a constant speed, the thrust should be equal to the drag, not greater than it. Therefore, statement D is not true according to Newton's law of inertia. After evaluating each statement, we can conclude that the correct answer is: (B) There are no unbalanced forces acting on the plane.

Key concepts

Understanding Unbalanced Forces

When learning about motion and mechanics in physics, particularly for the General Education Development (GED) test, it is crucial to grasp the concept of unbalanced forces. These play a pivotal role in changing the state of motion of objects.

What are Unbalanced Forces?

Unbalanced forces occur when two or more forces acting on an object do not cancel each other out, resulting in a net force. This net force sets the object into motion or changes its current motion. For instance, if a ball on the ground starts rolling when a person kicks it, the force of the kick is unbalanced, overcoming friction and the ball's inertia, which keeps it at rest.

Think of unbalanced forces as the reason for any change in motion: they start it, stop it, or alter its course. In the case of the exercising plane, it's mentioned that the plane moves at a constant speed and altitude. The balanced forces (thrust and drag, lift and weight) indicate that there are no unbalanced forces acting upon it—otherwise, the plane would accelerate, decelerate, or change direction, which is not the case.

Constant Velocity and Newton's First Law

A constant velocity means that an object is moving at the same speed and in the same direction. This term is often used interchangeably with constant speed, but in physics, velocity denotes both speed and direction. It's a vector quantity.

Newton's First Law and Motion

According to Newton's first law of motion, also known as the law of inertia, an object at rest stays at rest, and an object in motion stays in motion at a constant velocity unless acted upon by an unbalanced force. Applied to a real-world scenario like an airplane in flight, if the aircraft keeps a steady speed and altitude and travels in a straight line, the forces acting on it—namely gravity, lift, thrust, and drag—must be in equilibrium. This allows it to maintain its course smoothly, without unanticipated changes in motion. The 'no unbalanced forces' scenario (answer B) fits perfectly with Newton's first law.

Key Physics Concepts for the GED

The GED test includes a science section where understanding fundamental physics concepts is essential. One of the core ideas is mechanics—the study of motion and forces.

• Newton's Laws of Motion: These laws form the foundation for understanding how objects move and interact.
• Energy and Work: Knowing how work is performed and energy is transferred is another critical concept.
• Waves and Sound: Understanding the properties of waves and how sound is propagated helps in grasping the physics of everyday phenomena.
• Electricity and Magnetism: These topics cover the behavior of electric charges and the laws governing magnetic fields.

By familiarizing oneself with these topics, test-takers can better analyze and understand the forces and motions in various scenarios, making it easier to answer related questions on the GED test with confidence.