✔ 最佳答案
1. Weight of person = (30+50-4) kg = 76 kg
Let y be the distance of the person from the right scale.
Taking moment about the right scale,
clockwise moment = 50gx2 Nm (where g is the acceleration due to gravity)
anti-clockwise moment = (4x1 + 76y)g Nm
Equating clockwise and anti-clockwise moments
hence, 50x2 = 4x1 + 76y
this gives y = 96/76 m = 1.26 m
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2. Stress=force/cross-sectional area= 6.28/[pi x (0.1x10^-3)^2] N/m2
where pi=3.14159 ...
Strain = 0.2/100
Therefore, Young's modulus Y = stree/strain
Y = {6.28/[pi x (0.1x10^-3)^2]}/(0.2/100) N/m2 = 10^7 N/m2