You demonstrate hitting a board in a karate class. The speed of your hand as it hits the thick board is 20 m/s with respect to the board, and the mass of your hand is about 0.82 kg. How deep does your hand go into the board before stopping if the collision lasts for 2.0×10−3s?

Answer 1

V = Vo + a*t = 0.
20 + a*0.002 = 0,
a = -10,000 m/s^2.

V^2 = Vo^2 + za*d = 0.
20^2 + (-20,000)d = 0,
d = 0.02 m.