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Inga [223]
3 years ago
13

A speeding car is pulling away from a police car. The police car is moving at 30 m/s. The radar gun in the police car emits an e

lectromagnetic wave with a frequency of 20.0 x 109 Hz. The wave reflects from the speeding car and returns to the police car where the frequency is measured to be 4750 Hz less than what was emitted. The speed of light is 3 x 108 m/s. How fast is the speeding car going?
Physics
1 answer:
Gekata [30.6K]3 years ago
6 0

Answer:

65.625 m/s

Explanation:

F=20\times 10^9 Hz

\Delta F=F_r-F_t=4750 Hz

c = Speed of light = 3×10⁸ m/s

Relative speed

v=\frac{\Delta F}{2F}\times c\\\Rightarrow v=\frac{4750}{2\times 20\times 10^9}\times 3\times 10^8\\\Rightarrow v=35.625\ m/s

Relative speed = 35.625 m/s

Velocity of speeder = Velocity of police car + Relative speed

⇒Velocity of speeder = 30 + 35.625 = 65.625 m/s

∴ Velocity of speeder is 65.625 m/s

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Answer:

A: The acceleration is 7.7 m/s up the inclined plane.

B: It will take the block 0.36 seconds to move 0.5 meters up along the inclined plane

Explanation:

Let us work with variables and set

m=5kg\\\\F_H=100N\\\\\mu=0.3\\\\\theta=37^o.

As shown in the attached free body diagram, we choose our coordinates such that the x-axis is parallel to the inclined plane and the y-axis is perpendicular. We do this because it greatly simplifies our calculations.

Part A:

From the free body diagram we see that the total force along the x-axis is:

F_{tot}=mg*sin(\theta)+F_s-F_Hcos(\theta).

Now the force of friction is F_s=\mu*N, where N is the normal force and from the diagram it is F_y=mg*cos(\theta).

Thus F_s=\mu*N=\mu*mg*cos(\theta).

Therefore,

F_{tot}=mg*sin(\theta)+\mu*mg*cos(\theta)-F_Hcos(\theta)\\\\=mg(sin(\theta)+\mu*cos(\theta))-F_Hcos(\theta).

Substituting the value for F_H,m,\mu, and \:\theta we get:

F_{tot}= -38.63N.

Now acceleration is simply

a=\frac{F_H}{m} =\frac{-38.63N}{5kg} =-7.7m/s.

The negative sign indicates that the acceleration is directed up the incline.

Part B:

d=\frac{1}{2} at^2

Which can be rearranged to solve for t:

t=\sqrt{\frac{2d}{a} }

Substitute the value of d=0.50m and a=7.7m/s and we get:

t=0.36s.

which is our answer.

Notice that in using the formula to calculate time we used the positive value of a, because for this formula absolute value is needed.

5 0
3 years ago
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A calorimeter contained 350.0 g of water [cp=4.18 J/(g °C)] at 24.0 °C. An electric current was passed through a heater placed i
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Cp shows the amount of energy needed to raise temperature by one degree for one gram of water. 

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4 0
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