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3 years ago

I'm new to brainy, but here is my question.

Physics

2 answers:

skad [1K]3 years ago

8 0

680 is the right answer

Fittoniya [83]3 years ago

7 0

Answer: 680 J

Explanation:

Andre's mechanical energy is given by:

$E=K+U$

where

K is the kinetic energy

U is the gravitational potential energy

The kinetic energy in this case is zero, because Andre is sitting, so its speed is zero: v=0, and the kinetic energy is

$K=\frac{1}{2}mv^2=\frac{1}{2}(77.1 kg)(0)^2=0$

The gravitational potential energy is instead

$U=mgh=(77.1 kg)(9.8 m/s^2)(0.90 m)=680.0 J$

So, the total mechanical energy is

$E=U=680.0 J$

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The speaker at the concert has the sound intensity level of 100 dB if we listen from the distance 5 m.How far from the speaker d

Mademuasel [1]

Answer:

$28.11m$ far from the speaker the intensity drops to 85 dB.

Explanation:

In the equation for the Decibel scale

$(1). \: \:\beta =10 log(\dfrac{I}{I_0})$

The ratio of the intensities can be written as

$\frac{I}{I_0} = \dfrac{\frac{P}{A} }{\frac{P}{A_0} }$

$\dfrac{I}{I_0} = \dfrac{A_0}{A}.$

And since

$A = 4\pi r^2$

and

$A_0 = 4 \pi r_0^2$ ,

$\dfrac{A_0}{A} = \dfrac{4 \pi r_0^2}{4 \pi r^2} = \dfrac{r_0^2}{r^2}$

meaning

$\dfrac{I}{I_0} = \dfrac{r_0^2}{r^2}.$

Putting this into equation (1), we get:

$\boxed{ (2).\: \: \beta = 10log(\dfrac{r_0^2}{r^2})}$

Now, if the intensity is 100 dB when the distance is 5 meters, we have:

$100dB=10 log(\dfrac{r_02}{(5m)^2})$

$10= log(\dfrac{r_0^2}{25})$

by taking both sides to the exponent:

$10^{10}= \dfrac{r_0^2}{25}$

$r^2 = 25 *10^{10}\\r = 5 *10^5$

Now equation (2) becomes

$\beta = 10log(\dfrac{25*10^{10}}{r^2})$

when the intensity level is 85 dB we have

$85 = 10log(\dfrac{25*10^{10}}{r^2})$

$8.5 = log(\dfrac{25*10^{10}}{r^2})$

take both sides to exponents and we get:

$10^{8.5} =10^{ log(\dfrac{25*10^{10}}{r^2})}$

$10^{8.5} =\dfrac{25*10^{10}}{r^2}$

$r^2 = \dfrac{25*10^{10}}{10^{8.5}}$

$\boxed{r = 28.11m}$

Thus, $28.11m$ far from the speaker the intensity drops to 85 dB.

7 0

3 years ago

Two tuning forks A and B when sounded together produce 5 beats per second. The tuning fork A has frequency 480Hz. The fork B is

BartSMP [9]

<h2>The frequency of tuning fork B is 475 Hz</h2>

Explanation:

The number of beats produced is equal to the frequency difference between the two tuning forks .

The frequency of A = 480 Hz

Thus the frequency of B can be = 485 or 475 Hz

When B is filed , its frequency increases and it start producing 2 beats with A .

Thus it frequency must be 475 Hz , by filing , it increases to 478 Hz .

By which it gives 480 - 478 = 2 beats per second .

This cannot happen with frequency 485 , because by filing this difference increases in place of decreasing .

5 0

4 years ago

A tank is full of oil weighing 40 lb/ft^3. The tank is an inverted right circular cone (with the base at the top) with a height

krok68 [10]

Answer:

26945.6 ft⋅lbf

Explanation:

Volume of Right Circular Cone = pi*(radius^2)*(height/3)

Pi*(4)*(5/3) = 20.94 ft^3

Density = Mass / Volume

Mass = Density*Volume

Mass = (40)*(20.94)

Mass = 837.6 lb

Work = Force*Height

Force = Mass*Acceleration

Acceleration will be gravitational acceleration

Work = (837.6)*(32.17)*(1)

Work = 26945.6 ft⋅lbf

8 0

3 years ago

George's highest target heart rate is 170. Yesterday on the stair stepper machine, his heart rate went to 172. What should he do

Kruka [31]

Take a break and catch his breath.

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4 years ago

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To a stationary, a bus moves south with a speed of 15 m/s. a man inside walks toward the front of the bus with a speed of 0.2 m/

marta [7]

It is 15.2 m/s South.

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3 years ago

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