Answer:
Maximum compression; Δx = 0.003 m
Explanation:
The velocity of the bar when it hits the ground is gotten from equation of motion;
v² = u² + 2gh
u is 0 m/s since it was dropped from rest.
Thus;
v² = 2gh
Now, we know that in an elastic collision, the energy is conserved throughout. Thus, the kinetic energy just before it hits the ground is equal to the stored potential energy when it is fully compressed.
Hence, we'll say;
KE = PE.
The kinetic energy is given by the formula;
KE = ½mv²
Thus; since v² = 2gh;
KE = ½m(2gh)
KE = m•g•h
Now,the bar is essentially a spring. Thus; Spring potential energy is given by the formula;PE = ½k*Δx².
Where Δx is change in length or distance after compression.
We also know that F = k•Δx.
Young's modulus is given by the formula; Y = stress/strain
Where stress = Force/Area = F/A
And strain = change in length/original length ; Δx/L
Thus, Y = (F/A)/(Δx/L) = FL/AΔx
Thus ;YA/L = F/Δx
From earlier, F = kΔx or F/Δx = k
Thus k = F/Δx = YA/L.
So for potential energy:
PE = ½k•Δx²
Thus;
PE = ½YA•Δx²/ L
Area = πR²
So,
PE = ½Y(πR²)(Δx²)/L
Since potential energy is equal to kinetic energy, thus;
PE = KE
½Y(πR²)(Δx²)/L = m a d
Making Δx the subject, we have;
Δx = √{2m•a•d•L/[YπR²]}
We are given;
Mass; m = 1.100 kg
Acceleration due to gravity;g = 9.81 m/s²
Height;h = 4.7m
Length of bar;L = 0.72m
Youngs modulus;Y = 6 x 10^(10) Pa = 6 x 10^(10) N/m²
Radius;R = 0.0065m
Δx = √{{2(1.1)(-9.81)(-4.7)(0.72)}/[(6 x 10^(10))*π(0.0065)²]}
Δx = 0.003 m