Answer:True
Explanation: The mechanical waves need a medium through which to transport energy because the perturbation travels inside of the medium so it needs molecules that connect elastically the displacement of the wave. For example the sound mainly uses the air molecules to transport the energy also the sound can be traveled in solid materials like metal rods.
Answer:
nothing travels faster than light
Example:
You’ll always see lightning before you hear it, because typically lightning will be a mile away, two miles away.
Answer:

Explanation:
= Force on one side of the door by first waiter = 257 N
= Force on other side of the door by second waiter
= distance of first force by first waiter from hinge = 0.567 m
= distance of second force by second waiter from hinge = 0.529 m
Since the door does not move. hence the door is in equilibrium
Using equilibrium of torque by force applied by each waiter

Answer: 1000 Hz
Explanation:
You can calculate frequency by dividing velocity by wavelength
Frequency = velocity/wavelength
Find velocity first.
900 m/3 s = 300 m/s
Plug values in to find frequency.
F = (300 m/s)/0.3 m
F = 1000 Hz