Final answer:
Superman must apply a horizontal force of 28500 Newtons to give the boulder a horizontal acceleration of 15.0 m/s².
Step-by-step explanation:
To calculate the horizontal force that Superman must apply to the boulder, we can use Newton's second law of motion, which states that force equals mass times acceleration. In this case, the mass of the boulder is not given, but we can assume it is constant. The horizontal acceleration of the boulder is given as 15.0 m/s². Therefore, the equation becomes:
F = ma
where F is the force, m is the mass, and a is the acceleration.
Since the force applied by Superman is horizontal, it does not contribute to the vertical acceleration. Therefore, we only need to consider the horizontal force.
Let's assume the mass of the boulder is m. The force applied by Superman can be represented as Fhor, and the horizontal acceleration as ahor.
The equation can then be written as:
Fhor = mahor
Substituting the given values:
Fhor = 1900 N * 15.0 m/s² = 28500 N
Therefore, Superman must apply a horizontal force of 28500 Newtons to give the boulder a horizontal acceleration of 15.0 m/s².