Answer:
r₂ = 0.2 m
Explanation:
given,
distance = 20 m
sound of average whisper = 30 dB
distance moved closer = ?
new frequency = 80 dB
using formula
![\beta = 10 log(\dfrac{I_1}{I_0})](https://tex.z-dn.net/?f=%5Cbeta%20%3D%2010%20log%28%5Cdfrac%7BI_1%7D%7BI_0%7D%29)
I₀ = 10⁻¹² W/m²
now,
![30 = 10 log(\dfrac{I_1}{10^{-12}})](https://tex.z-dn.net/?f=30%20%3D%2010%20log%28%5Cdfrac%7BI_1%7D%7B10%5E%7B-12%7D%7D%29)
![\dfrac{I_1}{10^{-12}}= 10^3](https://tex.z-dn.net/?f=%5Cdfrac%7BI_1%7D%7B10%5E%7B-12%7D%7D%3D%2010%5E3)
![I_1= 10^{-8}\ W/m^2](https://tex.z-dn.net/?f=I_1%3D%2010%5E%7B-8%7D%5C%20W%2Fm%5E2)
to hear the whisper sound = 80 dB
![80 = 10 log(\dfrac{I_2}{10^{-12}})](https://tex.z-dn.net/?f=80%20%3D%2010%20log%28%5Cdfrac%7BI_2%7D%7B10%5E%7B-12%7D%7D%29)
![\dfrac{I_2}{10^{-12}}= 10^8](https://tex.z-dn.net/?f=%5Cdfrac%7BI_2%7D%7B10%5E%7B-12%7D%7D%3D%2010%5E8)
![I_2= 10^{-4}\ W/m^2](https://tex.z-dn.net/?f=I_2%3D%2010%5E%7B-4%7D%5C%20W%2Fm%5E2)
we know intensity of sound is inversely proportional to square of distances
![\dfrac{I_1}{I_2}=\dfrac{r_2^2}{r_1^2}](https://tex.z-dn.net/?f=%5Cdfrac%7BI_1%7D%7BI_2%7D%3D%5Cdfrac%7Br_2%5E2%7D%7Br_1%5E2%7D)
![\dfrac{10^{-8}}{10^{-4}}=\dfrac{r_2^2}{20^2}](https://tex.z-dn.net/?f=%5Cdfrac%7B10%5E%7B-8%7D%7D%7B10%5E%7B-4%7D%7D%3D%5Cdfrac%7Br_2%5E2%7D%7B20%5E2%7D)
![10^{-4}=\dfrac{r_2^2}{20^2}](https://tex.z-dn.net/?f=10%5E%7B-4%7D%3D%5Cdfrac%7Br_2%5E2%7D%7B20%5E2%7D)
r₂ = 0.2 m
Answer:
The volume of the block is equal to the volume of water displaced by the block.
Explanation:
Volume refers to the amount of space occupied by a given object (in this case the block). When an object such as the block is immersed in water, it displaces its own volume of water. This volume of water displaced is equal to the volume of the block. Hence we can write;
Final Volume of water - Initial Volume of water= Water Displaced = Volume of the block
Recall that the density of a body is given by;
Density= mass/volume
If we obtain the volume of the block by measuring the volume of water displaced by the block, then we weigh the block using a weighing balance, we can obtain the density of the block easily from the relationship shown above.
A convergent meniscus lens is a lens that is composed of two spherical surfaces, like the on shown next:
The imaginary line that runs through the middle of the lens is the "symmetry axis".
In this type of lenses incident parallel beams of light converge in one point, as follows:
And thus we get the diagram.
Answer:
speed of plane in still air = 1060 km/h
speed of wind = 170 km/h
Explanation:
Let teh speed of plane in still air is vp and the speed of air is va.
Irt travels 2670 km in 3 hours against the wind
So,
vp - va = 2670 / 3 = 890 km/h ..... (1)
It travels 11070 km in 9 hours along the wind.
vp + va = 11070 / 9 = 1230 km/h .... (2)
Adding both the equations
2 vp = 2120
vp = 1060 km/h
and va = 1230 - vp = 1230 - 1060 = 170 km/h
Answer:
5 hours
Explanation:
formula is 6 km per hour
if you have to travel 30 km, divide 30 by 6
30/6 = 5 hours