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+ <header style="text-align:center;">
+ <h2>Solutions of Savchenko Physics Textbook</h2>
+ <p class="author">
+ Aliaksandr Melnichenka <br/>
+ October 2023
+ </p>
+ </header>
+
+ <h3 id="back-link"><a href="../#1.1">$\leftarrow$Back</a></h3>
+
+ <h3> Statement </h3>
+ <p>
+ $1.1.19.$ By what angle will the direction of velocity of the ball change after two elastic impacts on the walls, the angle between which is equal to $\alpha$? How will the ball fly if the angle $\alpha = \pi/2$? The motion occurs in a plane perpendicular to the walls. In an elastic collision with a smooth stationary wall, the angle of incidence of the ball is equal to the angle of reflection.
+</p>
+<center>
+ <figure>
+ <img src="statement.png"
+ loading="lazy" width="250" />
+ <figcaption>
+ For problem $1.1.19$
+ </figcaption>
+ </figure>
+</center>
+<p>
+ </p>
+
+ <h3>Solution</h3>
+ <p>
+
+ <p>
+ When falling elastically on a horizontal plane, the angle of incidence is equal to the angle of reflection.
+ </p>
+ <center>
+ <figure>
+ <img src="01.png" alt="1.1.19"
+ loading="lazy" width="400" />
+ <figcaption>
+ The point of intersection of the perpendiculars drawn on the edge of the angle
+ </figcaption>
+ </figure>
+ </center>
+
+ <p>
+ Thus, the direction of velocity of the ball after two elastic impacts will change by the angle $\beta = 2\alpha$
+ </p>
+ <p>
+ When $\alpha=\pi/2$, $\beta = \pi$, i.e., the ball will fly in the opposite direction..
+ </p>
+ </p>
+
+ <h4>Answer</h4>
+ <p>
+ $β = 2α$. In the direction opposite to the initial
+ </p>
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