A box has a mass of 3 kg. The box is lifted from the floor and placed

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

A wave has a frequency of 655 he And is traveling at 455m/sec. what is the wavelength

Vlada [557]

Answer:

v=wavelength ×f

wavelength=v/f=455/655=0.694m

3 0

3 years ago

True or False: It would be easier to run on a planet with high gravity than one with less gravity.

LUCKY_DIMON [66]

True! It would be easier

3 0

3 years ago

A seesaw is 4.0m long with a pivot at its midpoint. A boy who weighs 400N sits at a distance of 1.5m from the pivot. His sister

bezimeni [28]

Answer:

the girl must sit 2 cm from the pivot at the opposite end of the seesaw.

Explanation:

Given;

length of the seesaw, L = 4.0 m

weight of the boy, W₁ = 400 N

position of the boy from the pivot, d₁ = 1.5 m

weight of her sister, W₂ = 300 N

First, make a sketch of this information given;

0---0.5m---------------------Δ--------------------------4m

↓<--------1.5m-------> <---------x--------->↓

400 N 300N

Apply the principle of moment about the pivot, to determine the value of x;

Sum of anticlockwise moment = sum of clockwise moment

400(1.5) = 300(x)

600 = 300x

x = 600/300

x = 2 cm

Thus, the girl must sit 2 cm from the pivot at the opposite end of the seesaw.

8 0

3 years ago

PLEASE HELP WILL GIVE BRAINLEST

mart [117]

1. Meiosis has 2 cell divisions but mitosis has only one cell division. Meiosis I is same as mitosis because parent cell produces diploid cells. But the difference between meiosis and mitosis is after the complete process meiosis produces genetically different haploid daughter cells and mitosis produces genetically same diploid daughter cells.

2. The main advantage of the sexual reproduction is It helps to produce offspring which can be well adapted to the environmental conditions due to the genetically differentiations. Hence, there are various types of offspring in the population. But the disadvantage is it requires two parents and it requires more time than asexual reproduction.

3. Advantages of asexual reproduction are it requires only parent, time for the process is relatively low, it produces genetically identical offspring. The main disadvantage is due to the production of genetically identical offspring, the survival rate is low when there is a disaster.

4. The organism can do either sexual reproduction or asexual reproduction to produce offspring. If it is difficult to find a partner to mate, the living being can do asexual reproduction to make offspring in a short period of time. When the organism needs genetically different offspring for survival, they can do sexual reproduction.

7 0

3 years ago

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