That's false. Mechanical waves (like sound and ocean waves) do
need a medium to travel in, but electromagnetic waves (like radio
and light) don't.
Answer:
6
Explanation:
The magnetic field inside a solenoid is given by the following formula:

where,
B = Magnetic Field Inside Solenoid
μ₀ = permittivity of free space
n = No. of turns per unit length
I = Current Passing through Solenoid
For Solenoid 1:

For Solenoid 2:
n₂ = 6n₁
Therefore,

Diving equation 1 and equation 2:

Hence, the correct option is:
<u>6</u>
Answer:
mu = 0.56
Explanation:
The friction force is calculated by taking into account the deceleration of the car in 25m. This can be calculated by using the following formula:

v: final speed = 0m/s (the car stops)
v_o: initial speed in the interval of interest = 60km/h
= 60(1000m)/(3600s) = 16.66m/s
x: distance = 25m
BY doing a the subject of the formula and replace the values of v, v_o and x you obtain:

with this value of a you calculate the friction force that makes this deceleration over the car. By using the Newton second's Law you obtain:

Furthermore, you use the relation between the friction force and the friction coefficient:

hence, the friction coefficient is 0.56