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3 years ago

Help with the two questions above? Correct answers?

Physics

1 answer:

LenKa [72]3 years ago

7 0

(6) first choice: the frequency appears higher and wavelength is shorter.

The car approaches a stationary observer and so the sound will appear to have shorter wavelength. This creates an effect of its siren to sound with higher frequency than it would do if both were stationary.

(7) The Doppler formula for frequency in the case of a stationary observer and source approaching it is as follows:

$f_O = \frac{v}{v-v_s}\cdot f= \frac{343\frac{m}{s}}{(343-25)\frac{m}{s}}\cdot 400Hz \approx 431Hz$

The wavelength is then

$\lambda = \frac{343\frac{m}{s}}{431Hz}\approx 0.80 m$

The third choice "0.80m; 431Hz" is correct

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On a cold winters da,y,If you left a drink setting outside,it could freeze.Explain why in a complete sentence

sertanlavr [38]

Hello!

On a cold winters day, if you left a drink setting outside, it could freeze because the heat (related to the kinetic energy) of the atoms in the drink will be transferred to the environment to achieve energy equilibrium.

Heat transfer occurs by various mechanisms, flowing from the hottest body to the coldest, that's why the heat goes from the drink, which has a higher temperature (and kinetic energy) to the environment, which has a lower temperature. This is described by the second law of thermodynamics

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Alex Ar [27]

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3 years ago

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What is the relationship between the frequency of light and its color?

shtirl [24]

Answer:

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3 years ago

A student on a skateboard is moving at a speed of 1.40 m/s at the start of a 2.15 m high and 12.4 m long incline. The total mass

saw5 [17]

Answer:

W = 609.97J

Explanation:

In order to calculate the work done by the student, you take into account that the total work is equal to the change of the kinetic energy of the student, as follow:

$W_T=\Delta K\\\\W+W_g-W_f=\frac{1}{2}m(v^2-v_o^2)\\\\W+Mgsin\alpha d-F_fd=\frac{1}{2}m(v^2-v_o^2)$ (1)

The work done by the friction force is negative because it is against the motion of the student.

W: work done by the student = ?

Wf: work done by the friction force

Wg: work done by the gravitational force

Ff: total friction force = 41.0N

m: mass of the skateboard = 53.0kg

d: distance traveled by the student

v: final speed of the student = 6.90m/s

vo: initial speed of the student = 1.40m/s

α: angle of the incline

You first calculate the distance d, with the Pythagoras' theorem

$d=\sqrt{(2.15m)^2+(12.4m)^2}=12.58m$

Furthermore, the angle α is:

$\alpha=tan^{-1}(\frac{2.15m}{12.4m})=9.83\°$

Then, you solve the equation (1) for W and replace the values of all parameters:

$W=\frac{1}{2}m(v^2-v_o^2)+F_fd-Mgsin\alpha d\\\\W=\frac{1}{2}(53.0kg)((6.90m/s)^2-(1.40m/s)^2)+(41.0N)(12.58m)\\-(53.0kg)(9.8m/s^2)sin(9.83\°)(12.58m)\\\\W=609.97J$

The work done by the student is 609.97J

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4 years ago

Given a circuit consisting of a DC battery of voltage 200 volts connected to a single resistor. If the electric current through

sertanlavr [38]

Given:

The battery voltage, V=200 V

The current through the resistor, I=50000 mA=50000×10⁻³ A

To find:

The resistance of the resistor.

Explanation:

From Ohm's law, the voltage across a circuit is directly proportional to the current through the circuit.

Thus the voltage across the resistor is given by,

$V=IR$

On substituting the known values in the above equation,

$\begin{gathered} 200=50000\times10^{-3}\times R \\ \Rightarrow R=\frac{200}{50000\times10^{-3}} \\ =4\text{ }\Omega \end{gathered}$

Final answer:

The resistance of the resistor is 4 Ω

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2 years ago