Which of the following is an example of projectile motion for an object launched horizontally (neglect air resistance)?

• A. A ball rolling across a level floor at constant speed
• B. A puck sliding on ice while a constant horizontal force is applied
• C. A ball thrown straight up and coming straight down along the same vertical line
• D. A ball rolling off the edge of a table and following a curved path to the floor

Answer: (D)

Verified step by step guidance

1. Understand the definition of projectile motion: it is the motion of an object that is launched into the air and moves under the influence of gravity alone, with no propulsion or additional forces acting on it (neglecting air resistance).
2. Identify the key characteristic of horizontal projectile motion: the object is launched with an initial horizontal velocity and simultaneously accelerates downward due to gravity, resulting in a curved, parabolic trajectory.
3. Analyze each option to see if it fits this description:
4. - A ball rolling across a level floor at constant speed experiences no vertical motion or acceleration due to gravity acting to change its vertical position, so it is not projectile motion.
5. - A puck sliding on ice with a constant horizontal force applied is influenced by an external force, so it is not free projectile motion.
6. - A ball thrown straight up and coming straight down moves only vertically, so it is not an example of horizontal projectile motion.
7. - A ball rolling off the edge of a table has an initial horizontal velocity and then falls under gravity, following a curved path, which matches the definition of horizontal projectile motion.