A stretched string long is fixed at both ends and vibrates in the fourth harmonic

PHYSICS · Single correct · A Level · Physics · Waves · Waves

Problem

A stretched string

1.20\,\mathrm{m}

long is fixed at both ends and vibrates in the fourth harmonic. At a point on the string, the displacement amplitude is

80\%

of the maximum possible amplitude. Which pair gives the two smallest distances of this point from the left end? (a)

0.06\,\mathrm{m}

and

0.24\,\mathrm{m}

(b)

0.09\,\mathrm{m}

and

0.21\,\mathrm{m}

(c)

0.12\,\mathrm{m}

and

0.18\,\mathrm{m}

(d)

0.07\,\mathrm{m}

and

0.17\,\mathrm{m}