Ask question

Ask question

All categories

4 years ago

9

A woman is riding a bicycle at 18.0 m/s along a straight road that runs parallel to and right next to some railroad tracks. She

hears the whistle of a train that is behind. The frequency emitted by the train is 840 Hz, but the frequency the woman hears is 778 Hz. Take the speed of sound to be 340 m/s.
(a) What is the speed of the train, and is the train traveling away from or towardt he bicycle?

(b) What frequency is heard by a stationary observer located between the train and the bicycle?

1 answer:

mr_godi [17]4 years ago

8 0

Answer:

(a) Speed of train is 7.66 m/s and it is traveling away from the bicycle.

(b) Frequency heard by the stationary observer is 821.50 Hz.

Explanation:

Doppler effect is defines as the change in the frequency of the wave as the observer and/or source are moving away or towards each other.

(a) According to the problem,

Speed of the observer, v₀ = 18 m/s

Speed of sound in air, v = 340 m/s

Original frequency emitted by train, f = 840 Hz

Apparent frequency heard by the observer, f₀ = 778 Hz

Let v₁ be the speed of the train.

Since, apparent frequency is less than original frequency i.e. f₀ > f . Hence, train are travelling away from the bicycle.

Thus, the Doppler effect equation is :

$f_{0} = (\frac{v - v_{0} }{v+v_{1} } )f$

Substitute the suitable values in the above equation.

$778 = (\frac{340 -18 }{340+v_{1} } )840$

340 + v₁ = 347.66

v₁ = 7.66 m/s

(b) In this case, speed of observer, v₀ = 0 m/s

Apparent frequency, $f_{0} = (\frac{v }{v+v_{1} } )f$

Substitute the suitable values in the above equation.

$f_{0} = (\frac{340 }{340+7.66 } )840$

f₀ = 821.50 Hz

You might be interested in

The section of the lever to the right of the fulcrum could be described as the?

ZanzabumX [31]

Answer:

Input Force

Explanation:

6 0

3 years ago

A space station that does not rotate cannot simulate gravity for its occupants.

il63 [147K]

false

true

false

false

true

4 0

3 years ago

A 25 kg circular disk has a diameter of 2.5 feet and a thickness of 2.5 cm. Find the density of the disk in kg/m3. Next, find th

Gre4nikov [31]

Answer:

Assume that $\rm g= 9.81\; N\cdot kg^{-1}$ ; $\rho(\text{Water}) = \rm 1000\;kg\cdot m^{-3}$ .

Density of the disk: approximately $\rm 2.19\times 10^{3}\; kg\cdot m^{-3}$ .

Weight of the disk: approximately $\rm 245\;N$ .

Buoyant force on the disk if it is submerged under water: approximately $\rm 112\; N$ .

The disk will sink when placed in water.

Explanation:

Convert the dimensions of this disk to SI units:

Diameter: $d = \rm 25\; inches = (25\times 0.3048)\; m = 0.762\;m$ .
Thickness $h = \rm 2.5\; cm = (2.5\times 0.01)\; m = 0.025\;m$ .

The radius of a circle is 1/2 its diameter:

$\displaystyle r = \rm \frac{1}{2}\times 0.762\;m = 0.381\; m$ .

Volume of this disk:

$V(\text{disk}) = \pi\cdot r^{2}\cdot h = \pi\times 0.381^{2}\times 0.025 \approx 0.0114009\; m^{3}$ .

Density of this disk:

$\displaystyle \rho(\text{disk}) = \frac{m}{V} = \rm \frac{25\; kg}{0.0114009\; m^{3}} = 2.19\times 10^{3}\;kg\cdot m^{-3}$ .

$\rho(\text{disk}) >\rho(\text{water})$ indicates that the disk will sink when placed in water.

Weight of the object:

$W(\text{disk}) = m\cdot g = \rm 25\times 9.81 = 245.25\; N$ .

The buoyant force on an object in water is equal to the weight of water that this object displaces. When this disk is submerged under water, it will displace approximately $\rm 0.0114009\; m^{3}$ of water. The buoyant force on the disk will be:

$\begin{aligned}F(\text{buoyant force}) &= W(\text{Water Displaced}) \\& = \rho\cdot V(\text{Water Displaced})\cdot g\\ & = \rm 1\times 10^{3}\; kg\cdot m^{-3}\times 0.0114009\; m^{3}\times 9.81\; N\cdot kg^{-1}\\ &\approx \rm 112\; N\end{aligned}$ .

The size of this disk's weight is greater than the size of the buoyant force on it when submerged under water. As a result, the disk will sink when placed in water.

3 0

3 years ago

9)A 64 kg parent and a 16 kg child meet at the center of an ice rink. They place their hands together and push. (A) Is the

Colt1911 [192]

Answer:

(A) <u>The same</u>

(B) <u>More</u>

(C) The magnitude of the parent's acceleration is 0.625 m/s²

Explanation:

The given parameters are;

The mass of the parent, m₁ = 64 kg

The mass of the child, m₂ = 16 kg

(A) By Newton's third law of motion, action and reaction are equal and opposite

Therefore, the action of the parent on the child is equal to the reaction of the child on the parent and vice versa

Therefore, the force experienced by the child is <u>the same</u> as the force experienced by the parent

(B) Newton's second law states that an objects acceleration is directly proportional to the applied force and inversely proportional to the mass of the object

Therefore, the parent and the child both experience the same force but the mass of the child is less than the mass of the parent and therefore, by Newton's second law, the acceleration of the child will be <u>more</u> than the acceleration of the parent for the same given force

(C) The acceleration of the child, a₂ = 2.5 m/s²

Let F₁ represent the force experienced by the parent, let F₂ represent the force experienced by the child and let a₁ represent the magnitude of the parent's acceleration

By Newton's third law, we have;

F₁ = F₂

Force, F = Mass, m × Acceleration, a

We can write, F = m × a

Therefore;

F₁ = m₁ × a₁ and F₂ = m₂ × a₂

∴ F₁ = F₂ gives;

m₁ × a₁ = m₂ × a₂

a₁ = (m₂ × a₂)/m₁ = (16 × 2.5)/64 = 0.625

∴ The magnitude of the parent's acceleration = a₁ = 0.625 m/s²

5 0

3 years ago

A rocket-driven sled Sonic Wind No. 2, is used for investigating the physiological effects of large accelerations on people. It

rewona [7]

Answer:

The best single equation in order to fin the acceleration is

$a=v_f/t=250/2=125m/s^2$

Explanation:

The best single equation in order to find the acceleration is the following kinematics equation:

$v_f=v_o+at$

As the rocket start from the rest, the initial velocity value is zero. Then the acceleration value is:

$a=v_f/t=250/2=125m/s^2$

7 0

3 years ago