The maximum possible height of a mountain on Earth is approximately (elastic limit of mountain rock $= 30 \times 10^7 \ N m^{-2}$,average density of mountain rock $= 3 \times 10^3 \ kg m^{-3}$,$g = 10 \ m s^{-2}$). (in $km$)

$A$ sphere of mass $4 \,kg$ is attached to one end of a steel wire of length $1 \,m$ and radius $1 \,mm$. It is whirled in a vertical circle with an angular velocity $10 \,rad \,s^{-1}$. If the sphere is at the lowest point of its path,the elongation in the wire is . . . . . . $(g=10 \,ms^{-2}, Y_{\text{steel}}=20 \times 10^{10} \,Nm^{-2})$ (in $\,mm$)

For the tensile stress on the cross-section $PQRS$ to be maximum,$\theta =$ ......... $^o$

An elevator cable can have a maximum stress of $7 \times 10^7\,N/m^2$ for appropriate safety factors. Its maximum upward acceleration is $1.5\,m/s^2$. If the cable has to support the total weight of $2000\,kg$ of a loaded elevator,the minimum area of cross-section of the cable should be ....... $cm^2$ $(g = 10\,m/s^2)$.

Two strips of metal are riveted together at their ends by four rivets,each of diameter $6.0\; mm$. What is the maximum tension that can be exerted by the riveted strip if the shearing stress on the rivet is not to exceed $6.9 \times 10^{7}\; Pa$? Assume that each rivet is to carry one quarter of the load.

If the breaking stress of a wire is $3.18 \times 10^{10} \, N/m^2$,what should be its minimum radius so that the wire does not break? (Refer to the figure for the masses attached to the pulley system,assume $g = 10 \, m/s^2$)