What is the average strain in a steel spike when struck by a 30kg sledge hammer?

AI Thread Summary
The discussion focuses on calculating the average strain in a steel spike when struck by a 30kg sledge hammer. The hammer's initial and rebound speeds, along with the time of impact, are provided for the calculations. Participants clarify the use of momentum change over time to determine force instead of initial velocity changes. Young's modulus for steel is noted as 2 x 10^11, which is essential for calculating strain. The conversation emphasizes the importance of understanding the correct formulas for accurate results in physics problems.
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A 30kg sledge hammer strikes a steel spike of 2.30 cm diameter while moving at 20.9 cm/s. The hammer rebounds with a speed of 10.0 cm/s after 0.110 s. What is the average strain in the spike during impact?



2. F = (mvf-mvi)/t
S = (F/A)/(deltaL/initialL)
Young's modulus for steel = 2 x 10^11




3. I used (vf-vi)/t to find the force but apparently I'm supposed to use change in momentum/time. I don't understand why.
 
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nevermind, i got it.
 
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