Q: Given below are some functions of x and t to represent the displacement of an elastic wave.

(i) y = 5 cos(4x) sin(20t)

(ii) y = 4 sin(5x – t/2) + 3 cos(5x – t/2)

(iii) y = 10 cos[(252 – 250)πt]cos[(252+250)πt]

(iv) y = 100 cos(100πt + 0.5x)

State which of these represent

(a) A travelling wave along – x-direction

(b) A stationary wave

(c) Beats

(d) A travelling wave along – x-direction

Ans: (a),(b),(c) & (d)