During aerobic exercising, people often suffer injuries to knees and other joints due to HIGH ACCELERATIONS. When do these high accelerations occur?

Estimate the acceleration you subject yourself to if you walk into a brick wall at normal walking speed.

(Make a reasonable estimate of your speed and of the time it takes you to come to a stop.)

A man drops a baseball from the edge of a roof of a building. At exactly the same time another man shoots a baseball vertically up towards the man on the roof in such a way that the ball just barely reaches the roof. Does the ball from the roof reach the ground before the ball from the ground reaches the roof, or is it the other way around?

Estimate the time it takes for a free fall drop from 10 meters height. Also estimate the time a 10 m platform diver would be in the air if he takes off straight up with a vertical speed of 2 m/s (and clears the platform of course!)