Question

The point (s) moving upward is/are:

• A. k
• B. C
• C. F
• D. G

Answer 1

The correct option is D G

Equation of the travelling wave is given by:
$y=Asin(-kx-\omega t)$ (moving along negative x axis)
Differentiating wrt time.
$v=A\omega cos(kx-\omega t)$ Since we are taking a snap we consider one such time.
With no loss of generality we take t = 0.
$v=A\omega cos\left(kx\right)$
For the point to move upward, velocity must be positive.
or kx must lie between $0and\frac{\pi }{2}$ and $\frac{3\pi }{2}and2\pi$
Points A and G satisfy this condition.