For the karate chop in the figure (Figure 1) , assume that the hand has a mass o
ID: 1368493 • Letter: F
Question
For the karate chop in the figure (Figure 1) , assume that the hand has a mass of 0.36 kg and that the speeds of the hand just before and just after hitting the board are 14 m/s and 0, respectively.
A) What is the average force exerted by the fist on the board if the fist follows through, so the contact time is 3.5 ms ? Express your answer using two significant figures.
B) What is the average force exerted by the fist on the board if the fist stops abruptly, so the contact time is only 0.29 ms? Express your answer using two significant figures.
Explanation / Answer
(a)
Use the equation for impulse:
I = m ( v ) / t
= m(vi - v0)/t
Substitute given values
I = 0.36 kg ( 14 m/s - 0 ) / ( 3.5 x 10-3 s )
= 1.4 x 103 N
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( b )
Substitute given values in I = m(vi - v0)/t
I = 0.36 kg ( 14 m/s - 0 ) / ( 0.29 x 10-3 s )
= 1.7 x 104 N