Original: The forces required to do this are quite large: to remove a foot from quicksand at a speed of .01 m\/s would require the same amount of force as "that needed to lift a medium-sized car."
Simplified: The forces required to do this are quite large: to remove a foot from quicksand at a speed of one centimeter per second would require the same amount of force as "that needed to lift a medium-sized car."