A new type of personal scale is designed where the person stands on top of a pla

Question

A new type of personal scale is designed where the person stands on top of a platform supported by a rubber cylinder which has a radius of 5 cm and a height of 10 cm. When one particular person stands on top of the platform the scale registers that the rubber cylinder is compressed by 1.4 cm. Young's modulus for rubber is 1.0E6 Pa.
(a) What is the mass of the person?
112

112 kg

(b) The person from part (a) is seen to jump into the air such that his acceleration while in contact with the platform is exactly equal to g, but in the upward direction. How much does the rubber compress in this situation?
2.8

2.8 cm

*Have the answers but can't find my work, and can't figure out how to do it now!

Explanation / Answer

a)Y=FL/AL

F=YAL/L=1*106 *3.14*5*5*10-4 *1.4*10-2 /*10*10-2

               =1099N

mass of the person m=F/g=1099/9.8=112.4kg

b) here his accleration is in upward direction and equel to g

ma=ma1 -mg              ,mg=ma1 -mg

ma1 =2mg this is the fforcce acting on the spring

L=FL/YA=2*112*9.8*10*10-2 /1*106 *3.14*5*5*10-4 =2.8cm

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