To find the magnitude of acceleration at the highest point of the projectile's path, we need to consider the forces acting on the projectile.
At the highest point, the vertical component of the projectile's velocity is momentarily zero. This means that the only force acting on the projectile in the vertical direction is gravity, pulling it downward. At this point, the projectile is momentarily at rest in the vertical direction.
The acceleration due to gravity is constant and always acts vertically downward near the Earth's surface. Its magnitude is approximately 9.8 m/s².
Since there are no other forces acting in the vertical direction at the highest point, the magnitude of the acceleration at this point is equal to the magnitude of the acceleration due to gravity, which is approximately 9.8 m/s².