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 car skids to a stop with locked brakes and leaves skid marks 30 m long. What information about the car would the police need to get to be able to estimate how fast the car was traveling when the driver slammed on the brakes?

A basketball player jumps 1 meter high off the ground, turns around and starts back down.

Estimate the time she is within 30 cm of the top of her trajectory (her hang time.)

(HINT: Calculate the time it takes to fall 30 cm from rest and double it.)

Explain why that works.