Factual error: When Kirk falls off El Capitan, he is shown falling all the way past the tops of the trees. I have been to Yosemite and the trees are tall, but not tall enough to give Spock enough time to slow then stop Kirk's fall.
By the time Kirk reaches the top of the trees, he is traveling at terminal velocity (assuming Kirk was halfway up, about 2000 feet from the ground, and an initial fall rate of 32 feet per second, per second), approximately 120 mph, about 200 feet per second. If the trees were 1000 feet tall and Spock caught Kirk right at the top of the trees, that would give him 5 seconds to slow down and stop Kirk. Impossible. Fortunately, in the movie he was able to accomplish this feat, or it would have been a very short movie. :).
