Any projectile always has a constant vertical acceleration of
a. 9.81 m. s^2
b. 0 m/s^2
c. -9.81 m/s^2
d. it is not constant.

The answer to your question is: C. -9.81 m/s²

Explanation:

A. 9.81 m/s²  acceleration is considered positive when it goes to the center of the earth, so this option is incorrect.

B. 0 m/s²  This option is incorrect because acceleration is 0 for a linear motion without acceleration.

C. -9.81 m/s²  If a projectile goes to the sky, then the acceleration will be negative.

D. It is not constant. Acceleration is constant.

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray