Answer:
The frequency of these waves is 
Explanation:
Given that,
Wavelength = 6.6 km
Distance = 8810 km
Time t = 8.67 hr
We need to calculate the velocity of sound
Using formula of velocity

Where, D = distance
T = time
Put the value into the formula


We need to calculate the frequency
Using formula of frequency


Put the value into the formula





Hence, The frequency of these waves is 
The type of ions that electrons collide with to cause resistance in a circuit is B. Metallic
Force = mass x acceleration
Here we have mass and a force so we are solving for acceleration:
Isolate for acceleration in the equation
Force / mass = acceleration
Fill in the equation:
250 / 70 = acceleration
Acceleration = 3.57 m/s^2