In a transverse wave,the particles of the medium:

The angle between the particle velocity and wave velocity in a transverse wave is [except when the particle passes through the mean position].

What are called mechanical waves?

Which type of waves can propagate in solids?

Given below are some examples of wave motion. State in each case if the wave motion is transverse,longitudinal or a combination of both:
$(a)$ Motion of a kink in a longitudinal spring produced by displacing one end of the spring sideways.
$(b)$ Waves produced in a cylinder containing a liquid by moving its piston back and forth.
$(c)$ Waves produced by a motorboat sailing in water.
$(d)$ Ultrasonic waves in air produced by a vibrating quartz crystal.

Which of the following waves cannot travel in a vacuum?