PHYSICS HIGH SCHOOL

As a bat flies toward a wall at a speed of 6.0 m/s, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?

Answers

Answer 1

Answer:

Answer:

$f_b = 29.98 Hz$

Explanation:

speed of bat = 6 m/s

sound wave frequency emitted by bat = 30.0 kHz

as we know,

speed of sound (c)= 343 m/s

$f_w = f((c+v_r)/(c+v_s))$

$f_w = 30((343+0)/(343+6))$

$f_w = 29.48 Hz$

now frequency received by bat is equal to

$f_b = f((c+v_r)/(c+v_s))$

$f_b = 29.48((343+6)/(343+0))$

$f_b = 29.98 Hz$

hence the frequency hear by bat will be 29.98 Hz

Answer 2

Answer:

Final answer:

The Doppler effect represents the change in frequency of a wave due to the motion of the source or the observer. In this case, the bat hears a higher frequency because of its motion towards the wall and the reflection of the sound wave back towards it.

Explanation:

The question is asking for the frequency the bat hears when it emits a sound and the sound is reflected back after hitting a wall. This is an example of the Doppler effect, where the frequency of a wave changes for an observer moving relative to the source of the wave.

Let's denote the emitted frequency as f (30.0 kHz), the speed of the bat as v (6.0 m/s), and the speed of sound in air as v_s (approximately 343 m/s).

First, when the bat emits the ultrasonic wave, the frequency of the wave will increase because of the motion of the bat towards the wall. The formula for observed frequency (f') when source and observer are getting closer is given by f' = f * (v_s + v) / v_s.

Next, the wall will reflect this wave back towards the bat. Since the wave is moving towards the bat, the frequency will increase again by the same factor, resulting in a final observed frequency of f'' = f' * (v_s + v) / v_s. When you substitute f' into this equation, you'll get: f'' = f * (v_s + v)^2 / v_s^2

Learn more about Doppler effect here:

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An internal combustion engine uses fuel, of energy content 44.4 MJ/kg, at a rate of 5 kg/h. If the efficiency is 28%, determine the power output and the rate of heat rejection

Answers

Efficiency = Power Output / Power Input

Power Input = Rate of Energy input = 44.4 MJ/kg * 5 kg/h

= 222 MJ/h

But 1 hour = 3600seconds

222 MJ/h = 222 MJ/3600s = 0.061667 MW J/s = Watts

Power input = 0.061667 MW = 61 667 W

From Efficiency = Power Output / Power Input

   28% = Power Output / 61667

   Power Output = 0.28 * 61667

   Power Output = 17266.76 W

Power Output = 17 267 W

Rate of heat Rejection = Power input - Power output

      = 61667 - 17267 = 44400 W

Rate of heat Rejection = 44 400 W.

C- Copyright.

A force is applied to a 30-kg object, resulting in an acceleration of 15 m/s. What is the force being applied to the object?

Answers

The sum of all forces applied to the object = (mass) x (acceleration)

The sum of all forces applied to the object = (30) x (15)

= 450 newtons, in the direction of the acceleration.

From Second Newton's Law:

F=a*m
a= $15 (m)/( s^(2) )$
m=30kg

F= $15 (m)/( s^(2) )$ *30kg=450N

pulls a wagon a distance of 32 meters the handle is above an angle of 20 degrees above horizontal if you pull on it with a force of 27 N what work is it

Answers

Hi there!

When finding work (J) given force (N), we use the equation:

W = FdcosФ <-- Only take into account the force in the direction of motion

Plug in the given values:

W = 27(32)cos(20) = 811.89 J

$\sf{work~done=811.89~J }$

Explanation:

Here,

Giventhat,

pulls a wagon a distance of 32 meters the handle is above an angle of 20 degrees above horizontal if you pull on it with a force of 27 N

Tofind,

The total work done

Aswe know that,

${\boxed{\sf{W=f.d.cos\theta }}}$

Accordingtothe question,

$W=27(32)cos{20}\n\nw=811.89J$

What is the minimum coating thickness (but not zero) that will minimize the reflection at the wavelength of 705 nm where solar cells are most efficient?

Answers

Answer:

d = 235 nm.

Explanation:

Let the layer be of glass. Refractive index of glass μ = 1.5. Let the required thickness be d.

For minimum reflection , that is destructive interference in thin films , the condition is

2μd = λ ( for first order)

d = 705 / 2 x 1.5 = 235 nm [ λ =705 nm ]

A boy cycles a distance of 960 m from home to school in 6 minutes. Calculate his average speed for the journey. Write your answer in m/s.

Answers

The average speed of the boy was 2,67m/s.

The average speed is found when we divide the distance traveled (Δx) by the travel time (Δt).

The formula is:

$\Huge\boldsymbol{V_(av)=(\Delta x)/(\Delta t)}$

Solving:

Data:

Distance: 960m

Time: 6min ⇒ (6 · 60) ⇒360s

We have:

$\LARGE\text{$V_(av)=(960)/(360)$}\n\n\n\n\Huge\boldsymbol{V_(av)\approx2,67m/s}$

The average speed of the boy for his journey is approximately2,67m/s.

_________

Know more:

About speed:

Hope this helps!

To calculate the average speed of the boy's journey, you can use the formula:

Average Speed (in m/s) = Distance (in meters) / Time (in seconds)

First, you need to convert the time from minutes to seconds because 1 minute equals 60 seconds:

6 minutes = 6 * 60 seconds = 360 seconds

Now, you can calculate the average speed:

Average Speed = 960 meters / 360 seconds = 2.67 m/s

So, the boy's average speed for the journey is approximately 2.67 meters per second.

Explain how machines make work easier if they still require that the same amount of work be done.

Answers

Machines make work easier even if they still require the same amount of work to be done. We humans get tired because we do not have constant source of energy for the work to be done.Machines have a constant source of energy such as electricicity. Humans too will work at the same rate without getting tired if they are also provided with constant energy.

well machine do not feel pain of course and us humans and people do feel pain of course but if we fell pain and get hurt it slows down the process but machines on the other hand can keep going until the life source runs out. if i helped plz make mine the best

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