Science ck-12 green house effect

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 0.8 m length of wire is formed into a single turn, square loop in which there is a current of 12 A. The loop is placed in magn

rewona [7]

Answer:

0.073 N-m

Explanation:

i = 12 A, l = 0.8 m, B = 0.12 T

The circumference of the loop is 0.8 m.

Let r be the radius of the loop.

2 x 3.14 x r = 0.8

r = 0.127 m

Maximum Torque = i x A x B

Maximum Torque = 12 x 3.14 x 0.127 x 0.127 x 0.12 = 0.073 N-m

8 0

4 years ago

A person who is good at caring for others might enjoy a career as a

julia-pushkina [17]

He or she would enjoying doing a job as a caretaker

5 0

4 years ago

How do scientists know the true environmental lapse rate in a column of air?

stepan [7]

With weather ballons carry instruments to measure the temperature ,pressure,wind direction and wind speed

3 0

4 years ago

The isotope 23893Np has a half-life of 2.0 days. If 4.00 grams are produced at noon on Monday, what will be the mass of neptuniu

viva [34]

Answer:

0.25 gram of neptunium is remaining

Explanation:

First we calculate the no. of half lives passed. For that we have formula:

n = t/T

where,

n = no. of half lives passed = ?

t = total time passed = 8 days (From Monday noon to Tuesday noon of following week)

T = Half Life Period = 2 days

Therefore,

n = 8 days/2 days

n = 4

Now, for the remaining mass of neptunium, we use the formula:

m = (mi)/(2)^n

where,

mi = initial mass of neptunium = 4.00 grams

m = remaining mass of neptunium = ?

Therefore,

m = 4 grams/2⁴

3 0

3 years ago