What is the vertical acceleration a_y near Earth's surface under gravity, taking upward as positive?

What is the vertical acceleration a_y near Earth's surface under gravity, taking upward as positive?

• A. A_y = g
• B. A_y = 0
• C. A_y = -g
• D. A_y = -2g

Answer: (C)

Gravity near Earth’s surface pulls objects downward with a constant acceleration of magnitude g. Since upward is positive, downward acceleration is negative, so the vertical component is a_y = -g (about -9.8 m/s^2). This reflects that gravity accelerates everything downward, and the sign simply comes from the chosen upward positive direction. The other possibilities would imply upward acceleration, no acceleration, or a force twice as strong, which does not describe gravity in this context.

Gravity near Earth’s surface pulls objects downward with a constant acceleration of magnitude g. Since upward is positive, downward acceleration is negative, so the vertical component is a_y = -g (about -9.8 m/s^2). This reflects that gravity accelerates everything downward, and the sign simply comes from the chosen upward positive direction. The other possibilities would imply upward acceleration, no acceleration, or a force twice as strong, which does not describe gravity in this context.