Young's Modulus (Finding Average Strain)

[Big-oh]

Homework Statement

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?

Mass of hammer = 30 kg
Radius of Spike = 1.15 cm or 0.0115m
Initial speed of hammer = 0.209 m/s
Final speed of hammer = 0.100 m/s
Time of impact = 0.110 s

Homework Equations

Y = Stress / Strain
Stress = Force Applied / Area Perpendicular
Inertia = Force * (Delta Time) = Change in Momentum = Mass * (Delta Speed)

The Attempt at a Solution

Manipulating the Inertia equations, I got that

Force = (Mass * (Delta Speed))/(Delta Time)

Dividing that by the Area of the head of the steel spike gives me the average stress during this time.

(Stress came out to be 2.03*10^5 N/m^2 for me)

I am confused as to how to find out the average strain without the Modulus of the steel spike. :/

 

[rock.freak667]

You might just need to look up the modulus of elasticity of steel and use it, otherwise, you can't really find it. It should be around 200 GPa if I remember correctly.