The two wires shown in figure are made of the same material which has a breaking stress of `8xx10^8Nm^-2`. The area of cross section of the upper wire is `0.006 cm^2` and that of the lower wire is `0.003 cm^2`. The mass `m_1=10 kg`, `m_2=20kg` and the hanger is light. a. Find the maximum load that can be put on the hanger without breaking a wire. Which wire will break first if the load is increased? b. Repeat the above part `m_1=10 kg and m_2=36kg`.

Answer

A, D

Explanation

`sigma_(max)` on upper string `= ((m_(1)+m_(2)+m)g)/(0.006xx10^(-4))`
`:. 8xx10^(8) = ((10+20+m)xx10)/(0.006xx10^(-4))`
or `m = 18 kg`
`sigma _(max) ` on lower string `= ((m_(1)+m')g)/(0.003xx10^(-4))`
or ` m' = 14 kg`
So, answer is `14 kg` and lower string will break earlier.