AP Physics C: Karate Expert's Board Chop Calculation

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SUMMARY

The discussion focuses on a physics problem involving a karate expert breaking a pine board with a hand chop. The board is 2.2 cm thick, and the expert's hand, weighing 580 g, strikes at a speed of 9.5 m/s, coming to rest 2.8 cm below the board's top. Participants calculated the time duration of the chop and the average force applied, utilizing the equations of motion and Newton's second law (F=ma). A key point of contention was the correct interpretation of the displacement for the velocity-acceleration equation.

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CoreanJesus
1. The problem statement, all variables and given/known
A karate expert breaks a pine board, 2.2 cm thick, with a hand chop. Strobe
photography shows that his hand, whose mass may be taken as 580 g, strikes the
top of the board with a speed of 9.5 m/s and comes to rest 2.8 cm below this level.
(a) Calculate the time duration of the chop (assuming a constant force). (b)
Calculate the average force applied.


Homework Equations


Velocity position accel. equation and F=ma

The Attempt at a Solution


So I know the answer and I've solved it. But I don't understand for part a why you would use just .028m instead of .022+.028 for the delta y in your velocity accel. Poston function.[/B]
 
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The problem literally states that the 2.8 cm are relative to the top of the board.