Tissues types<br> Please help

A train whistle is heard at 300 Hz as the train approaches town. The train cuts its speed in half as it nears the station, and t

spin [16.1K]

Answer:

The speed of the train before and after slowing down is 22.12 m/s and 11.06 m/s, respectively.

Explanation:

We can calculate the speed of the train using the Doppler equation:

$f = f_{0}\frac{v + v_{o}}{v - v_{s}}$

Where:

f₀: is the emitted frequency

f: is the frequency heard by the observer

v: is the speed of the sound = 343 m/s

$v_{o}$ : is the speed of the observer = 0 (it is heard in the town)

$v_{s}$ : is the speed of the source =?

The frequency of the train before slowing down is given by:

$f_{b} = f_{0}\frac{v}{v - v_{s_{b}}}$ (1)

Now, the frequency of the train after slowing down is:

$f_{a} = f_{0}\frac{v}{v - v_{s_{a}}}$ (2)

Dividing equation (1) by (2) we have:

$\frac{f_{b}}{f_{a}} = \frac{f_{0}\frac{v}{v - v_{s_{b}}}}{f_{0}\frac{v}{v - v_{s_{a}}}}$

$\frac{f_{b}}{f_{a}} = \frac{v - v_{s_{a}}}{v - v_{s_{b}}}$ (3)

Also, we know that the speed of the train when it is slowing down is half the initial speed so:

$v_{s_{b}} = 2v_{s_{a}}$ (4)

Now, by entering equation (4) into (3) we have:

$\frac{f_{b}}{f_{a}} = \frac{v - v_{s_{a}}}{v - 2v_{s_{a}}}$

$\frac{300 Hz}{290 Hz} = \frac{343 m/s - v_{s_{a}}}{343 m/s - 2v_{s_{a}}}$

By solving the above equation for $v_{s_{a}}$ we can find the speed of the train after slowing down:

$v_{s_{a}} = 11.06 m/s$

Finally, the speed of the train before slowing down is:

$v_{s_{b}} = 11.06 m/s*2 = 22.12 m/s$

Therefore, the speed of the train before and after slowing down is 22.12 m/s and 11.06 m/s, respectively.

I hope it helps you!

7 0

3 years ago

Kevin has a mass of 87 kg and is skating with in-line skates. He sees his 22-kg younger brother up ahead standing on the sidewal

neonofarm [45]

Answer:

$V_ k = 3 m/s$

Explanation:

Using the conservation of the linear momentum P:

$P_i = P_f$

so:

$M_kV_k = M_sV_s$

where $M_k$ is the mass of kevin, $V_k$ is the velocity of kevin before he grabs her brother, $M_s$ is the velocity of her brother and him after grabs her brother and $V_s$ is the velocity of both after the collition.

So, replacing the values and solving for Vk, we get:

$(87 kg)V_k = (87 kg+22 kg)(2.4m/s)$

$V_ k = 3 m/s$

8 0

3 years ago

On a frozen pond, a 8.54-kg sled is given a kick that imparts to it an initial speed of ð£0=1.87 m/s. The coefficient of kinetic

zhannawk [14.2K]

Answer:2.05 m

Explanation:

Given

Mass of sled $m=8.54 kg$

initial speed $u=0.187 m/s$

coefficient of kinetic Friction $\mu _k=0.087$

According to work-energy theorem work done by all the forces is change in Kinetic energy

$W_{friction}=\frac{1}{2}mv_i^2-\frac{1}{2}mv_f^2$

$\mu _kmg\times d=\frac{1}{2}\times 8.54\times 1.87^2$ ,where d= distance moved

$0.087\times 8.54\times 9.8\times d=14.93$

$d=\frac{14.93}{7.281}$

$d=2.05 m$

4 0

3 years ago

PLZ HELP

TEA [102]

Answer:

The ion has more protons than electrons.

Explanation:

6 0

3 years ago

What is a metallic bond?<br> Explain in like a simple way please

masya89 [10]

Metallic bond, force that holds atoms together in a metallic substance. ... The atoms that the electrons leave behind become positive ions, and the interaction between such ions and valence electrons gives rise to the cohesive or binding force that holds the metallic crystal together.

3 0

3 years ago

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Tissues types Please help