In projectile motion, a body that is given an initial velocity and then allowed to move only under the effect of gravitational acceleration is called what?

Introduction / Context:
This question tests your understanding of the basic definition of projectile motion in mechanics. Many problems in physics involve objects that are thrown, kicked or launched and then move under the influence of gravity alone, ignoring air resistance. These motions follow characteristic curved paths known as trajectories. Knowing the correct term for such a body helps you classify problems and apply the correct kinematic equations in two dimensions.

Given Data / Assumptions:

• A body is given an initial velocity at some angle or along some direction.
• After launch, the only significant force acting on the body is the gravitational force of the Earth.
• Air resistance and other forces are neglected for simplicity.
• The options include projectile, satellite, pendulum bob and free electron.

Concept / Approach:
A projectile is defined as any object that is projected into space with an initial velocity and then allowed to move under the influence of gravity alone. Its path is determined by its initial speed, launch angle and gravitational acceleration. Typical examples include a thrown ball, a bullet fired horizontally (ignoring air drag) or a stone launched from a catapult. Satellites, while also under gravity, are in continuous free fall around the Earth and involve orbital mechanics rather than simple projectile motion. A pendulum bob is constrained by a string, and a free electron in a conductor is influenced by electric fields, not purely by gravity. Therefore, the correct term is projectile.

Step-by-Step Solution:
Step 1: Recall that projectile motion occurs when an object is launched and then moves freely under gravity, with no propulsion and negligible air resistance. Step 2: Recognise that this situation matches the description given: initial velocity followed by motion only under gravity. Step 3: Identify that the standard term for such a body is projectile, and that its trajectory is typically a parabola near the Earth surface. Step 4: Compare this with satellites, which undergo orbital motion, and pendulums, which are constrained by strings and experience tension forces as well as gravity. Step 5: Note that a free electron in a conductor primarily responds to electric fields and collisions, not just gravitational acceleration. Step 6: Conclude that the correct answer is projectile.

Verification / Alternative check:
In textbook chapters on projectile motion, the first definition usually states something like: any object thrown into space with an initial velocity and then moving under the action of gravity alone is called a projectile. Diagrams of cannon shells, balls and arrows are then used to illustrate curved trajectories. Satellites are treated separately under gravitation and planetary motion, where the curvature of the Earth and orbital speed are crucial. This clear separation in teaching materials confirms that the term you need in this context is projectile.

Why Other Options Are Wrong:
A satellite in orbit is under gravity but moves fast enough to keep missing the Earth, leading to orbital motion rather than the simple projectile path assumed in elementary problems. A simple pendulum bob is attached to a string and experiences tension as well as gravity, so its motion is not free projectile motion. A free electron in a conductor is strongly influenced by electric fields and collisions with atoms, making its dynamics very different from a purely gravitational projectile.

Common Pitfalls:
Some learners may overgeneralise and think that any object under gravity is a projectile, including satellites and pendulum bobs. However, in exam level mechanics, the term projectile is reserved for objects that move freely under gravity with no constraint forces like tension or continuous propulsion. Remembering examples like a thrown ball or a kicked football will help solidify the correct definition.

Final Answer:
A body given an initial velocity and then allowed to move only under gravity is called a projectile.