Figure shows a snapshot for a travelling sine wave along a string. Four elemental portions $a, b, c$ and $d$ are indicated on the string. The elemental portion which has maximum potential energy is/are

A rod of length $1.2\,m$ is clamped at the mid point and its fundamental frequency is $2\,MHz$ , then speed of wave inside the rod?

A second harmonic has to be generated in a string of length $l$ stretched between two rigid supports. The point where the string has to be plucked and touched are

Two wires are fixed in a sonometer. Their tensions are in the ratio $8 : 1$. The lengths are in the ratio $36:35.$ The diameters are in the ratio $4 : 1$. Densities of the materials are in the ratio $1 : 2$. If the lower frequency in the setting is $360 Hz.$ the beat frequency when the two wires are sounded together is

What will be the change in phase of wave due to reflection from rigid support ?

A piano string $1.5\,m$ long is made of steel of density $7.7 \times 10^3 \,kg/m^3$ and  Young’s modulus $2 \times 10^{11} \,N/m^2$. It is maintained at a tension which produces  an elastic strain of $1\%$ in the string. The fundamental frequency of transverse vibrations of string is ......... $Hz$