Get posts from category from custom query

I figured it out. Here is my solution

<?php 
    $categories = get_the_category();
    $category_id = $categories[0]->cat_ID;
    $mymain_query = new WP_Query( array( 'cat' => $category_id,'posts_per_page' => '10' ) ); while($mymain_query->have_posts()) : $mymain_query->the_post(); ?>

    //shortened code below
    <div class="blog-post">
        <h5><?php the_title(); ?></h5>
        <p><?php the_content(): ?></p>
    </div>

<?php endwhile; ?>
<?php wp_reset_postdata(); // reset the query ?>