Here's why:
* Gravity: When you throw something upwards, gravity acts against its motion, slowing it down.
* Zero Velocity at the Top: At the highest point of its trajectory, the projectile momentarily stops moving upwards before it begins to fall back down. This means its vertical velocity is zero at that point.
Important Note: While the projectile's vertical speed is zero at the top, it still has horizontal speed if it was thrown at an angle. However, the question specifically asks about *zero speed* at the top, which implies both vertical and horizontal velocity are zero. This can only be achieved by throwing straight upwards.
