Question

Estimate the force with which a karate master strike a board, assuming the hands speed at the moment of Impact is 10.0 $m{s}^{-1},$decreasing to 1.00 m $s^{-1}$ during a 0.002 s time internal of contact between the hand and the board. The mass of his hand and arm is 1.00 kg.

Answer 1

We will use the impulse momentum theorem to find the force on the hand, which is equal in magnitude to the force on the board. Then the definition of shear stress will let us compute that quantity to see if it is large enough to break the board. The impulse momentum theorem describes the force of the board on his hand:
$Fl=m{v}_2-m{v}_1$
$F\left(0.002s\right)=\left(1.00kg\right)(1.00m{s}^{-1}-10.0m{s}^{-1})$
and $F=-4500N$
a. Therefore, the force of his hand on board is 4500 N