Question

A ball is thrown up in the sky, at what position will the instantaneous speed be minimum?

• A. Final position
• B. Initial position
• C. Halfway between the initial position
• D. After reaching the ground and before impact

Answer 1

Answer: (A)

Final position

Answer 2

When a ball is thrown upwards, it moves against the force of gravity. Gravity continuously acts downwards, causing the upward component of the ball's velocity to decrease.

1. Upward Journey: As the ball ascends, its speed decreases.

2. Highest Point (Apex): At the peak of its trajectory, the ball momentarily stops moving upwards. Its vertical component of velocity becomes zero.

   • If the ball is thrown straight up, its total speed at this point becomes zero (the absolute minimum).

   • If the ball is thrown at an angle (projectile motion), its horizontal component of velocity remains constant throughout the flight (ignoring air resistance). At the highest point, the vertical component is zero, so the total speed is equal to the constant horizontal velocity. This horizontal velocity is the minimum speed the ball attains during its flight.

3. Downward Journey: After reaching the highest point, the ball starts falling downwards, and its speed increases due to gravity.

Therefore, the instantaneous speed of the ball is minimum at the highest point of its trajectory. Among the given options, "Final position" is the most appropriate choice if interpreted as the highest point of the upward motion.