Q:The equation of a wave pulse is given as $ \displaystyle y = \frac{0.8}{(4x+5t)+4} $ the amplitude and velocity of the pulse are

(a)0.2 units, 1.25 units along –ve x-axis

(b)0.2 units, 1.25 units along +ve x-axis

(c)0.4 units, 1.25 units along –ve x-axis

(d)0.4 units, 1.25 units along +ve x-axis

Ans: (a)

Sol: $ \displaystyle y_{max} = \frac{0.8}{4} = 0.2 m $

$\displaystyle 4 x + 5t = constant $

Differentiating w.r.t time

$ \displaystyle 4 \frac{dx}{dt} + 5 = 0 $

$ \displaystyle \frac{dx}{dt} = – \frac{5}{4} = – 1.25 m/s $