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Hi Qian, here my assignment of lecture 3. I hope you can read it! Kind regards, Jesse de Heij! :)

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Hi Qian, here my assignment of lecture 3. I hope you can read it! Kind regards, Jesse de Heij! :)

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Optional assignment lecture 3

Estimate the allowed weight of your plastic bag can hold.

δ=F/A0

δ=m×g/A0

m=?

m= δ×A0/g

A0=1×20×10-6=2×10-5 m2

g=9,81 m/s2

E= δ/e

125= δ/12

δ=1500

m=1500×2×10-5/9,81

m=3,06 ×10-3 kg

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Treksterkte LDPE: 11.7 mPa = 11.7 mN/m^2

m^2= 1*0.002= 0.002

N=0.002*11.7*10^3=23.4

23.4/9.81=2.4 kg _�U�퐧�

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Optional Homework lesson 3

The stress at 20% elongation is approximately 7MPa, that is 7 n/mm2. You have 1mx20mm of surface, that is 1000x20= 20 000mm2.

If you want to calculate the Force, you have to do A*δ

F= 20000*7= 140 000 N

If you want to have the mass, you devide it by g(9,81m/ss)
M=140000/9,81= 14 276 kg