Linear motion and D'Alemberts principle of equating forces (a metal press)

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Oliver

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Metal Press Task

A metal press has a mass of 479kg and falls through a vertical distance 'h' it strikes a bed of 300kg and is brought to rest after moving through a further distance of 67mm.
Gravity = 9.81m/s2

Determine the height the press falls 'h' given the resistance of the bed is 72140N assuming the resistive force of the metal to be uniform and the press does not bounce. The final velocity is zero.
 
This is my attempt at answering the question but I have been told that it is all wrong including the basic f=m*a calculation.

Press = 479kg
Bed = 300kg
D= 67mm =0.067m
Gravity = 9.81m/s2
Bed R = 72140N

Weight of press = 479 * 9.81 = 4698.99N
Net upward force = 72140 - 4698.99 = 67441.01N

f=m*a

67441.01 = 479 * a
a = 67441.01/479
=140.80m/s2
=-140.80m/s2 as the velocity is decreasing

Velocity just before collision with the bed
Vf2=Vi2 + 2 * a * D
Vi2 + 2 * -140.80 * 0.067 = 0
Vi2 = 18.867
Vi = √18.867 = 4.344m/s

Height of Press
Vf2 = Vi2 + 2 * a * D
Vf2 =18.867 Vi =0 a =9.81
18.867 = 2 * 9.81 * h
h = 18.867/19.62 = 0.9616m

But as I said apparently all this is wrong :sad:
 
Last edited:
Still stuck on this and I need to hand it in tomorrow. Can anyone help? Just pointing me i the right direction could help. Thanks
 
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