1. b
2. c
3. A. Those are the answers
Answer:
The atmospheric pressure is
.
Explanation:
Given that,
Atmospheric pressure
drop height h'= 27.1 mm
Density of mercury 
We need to calculate the height
Using formula of pressure

Put the value into the formula



We need to calculate the new height




We need to calculate the atmospheric pressure
Using formula of atmospheric pressure

Put the value into the formula


Hence, The atmospheric pressure is
.
Answer:
B.) by interfering with sound waves
Explanation:
As we know that the interference of sound waves is of two types
1). constructive interference
2). destructive interference
now we know that constructive interference means the resultant intensity will be more than the intensity of interfering waves as here two waves are in same phase.
In destructive interference the resultant of two waves is given by the minimum resultant of the intensity as here the phase of two waves are opposite to each other.
So we will say that

here in case of noise cancelling headphones we know that the phase of noise is always made in opposite phase with the sound which is used to cancelled the noise.
This will reduce the noise and we will get a clear sound
To solve this problem we will apply the concepts related to Ohm's law and Electric Power. By Ohm's law we know that resistance is equivalent to,

Here,
V = Voltage
I = Current
While the power is equivalent to the product between the current and the voltage, thus solving for the current we have,


Applying Ohm's law


Therefore the equivalent resistance of the light string is 
After traveling for 6.0 seconds, a runner reaches 10m/s. What is the runner's acceleration? Answer: 1.67 m/s2