The first person = A
The second one = B
velocity of A = 3 km / h
velocity of B = 4 km / h
Distance of A = 3t
Distance of B = 35 - 4t
At what time do they meet?
3t = 35 - 4t
7t = 35
t = 5 hours
7 a.m. + 5 hours = 12 p.m.
Remember that sound intensity decreases in inverse proportion to the distance squared. So, to solve this we are going to use the inverse square formula:

where

is the intensity at distance 2

is the intensity at distance 1

is distance 2

is distance 1
We can infer for our problem that

,

, and

. Lets replace those values in our formula to find

:





dB
We can conclude that the intensity of the sound when is <span>3 m from the source is
30 dB.</span>
Decibel<span> (dB) and, hearing loss levels can be anywhere like </span><span><span>-56 to -70 dB for Moderate/severe hearing loss, -</span><span>71 to -90 dB for Severe loss and</span><span> -91 dB for <span>Profound loss.</span></span></span>
Back emf is 85.9 V.
<u>Explanation:</u>
Given-
Resistance, R = 3.75Ω
Current, I = 9.1 A
Supply Voltage, V = 120 V
Back emf = ?
Assumption - There is no effects of inductance.
A motor will have a back emf that opposes the supply voltage, as the motor speeds up the back emf increases and has the effect that the difference between the supply voltage and the back emf is what causes the current to flow through the armature resistance.
So if 9.1 A flows through the resistance of 3.75Ω then by Ohms law,
The voltage across the resistance would be
v = I x R
= 9.1 x 3.75
= 34.125 volts
We know,
supply voltage = back emf + voltage across the resistance
By plugging in the values,
120 V = back emf + 34.125 V
Back emf = 120 - 34.125
= 85.9 Volts
Therefore, back emf is 85.9 V.