AP Physics C: Karate Expert's Board Chop Calculation

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The discussion revolves around a physics problem involving a karate expert breaking a pine board. The key variables include the board's thickness of 2.2 cm, the mass of the hand at 580 g, and the hand's striking speed of 9.5 m/s, which comes to rest 2.8 cm below the board's top. Participants are calculating the time duration of the chop and the average force applied, using the equations of motion and Newton's second law. A point of confusion arises regarding the displacement used in calculations, specifically whether to include the board's thickness in the total distance. Clarification is sought on why only the 2.8 cm is considered for delta y in the velocity-acceleration function.
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.
 
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