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Juliette [100K]
3 years ago
9

An extraterrestrial "Eratosthenes" performs the equivalent experiment, that Eratosthenes did on Earth, on her/his home world. Sh

e/He measures the angle of the shadow in her/his alien hometown (Alexandria) to be 10 degrees and the distance to the alien well (Syene) to be 500 km. What is the radius that the alien Eratosthenes estimates for her/his planet?
a. 2865 km
b. 9065 km
c. 18024 km
d. 1500 km
e. 31415 km
Physics
1 answer:
Bad White [126]3 years ago
6 0

Answer:

a. 2865 km

Explanation:

Eratosthenes observed that the sun's rays formed a vertical angle of 7º 12 ’. Which confirmed that the Earth was not flat, assuming that it had a spherical shape, using the distance between Alexandria and Siena and the measure of the angle of inclination of the solar rays in Alexandria, calculated the circumference of the Earth.

The calculation was made with a simple rule of three:

angle of inclination of the solar rays——————- distance

               360º                                   ————- Planet circumference

C=\frac{distance*360^\circ}{angle}\\\\C=\frac{500km*360^\circ}{10^\circ}=18000km

And since we know that:

C=2\pi R\\\\R=\frac{C}{2\pi}\\\\R=\frac{18000km}{2\pi}=2865km

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Suppose a police officer is 1/2 mile south of an intersection, driving north towards the intersection at 40 mph. At the same tim
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Answer:

75.36 mph

Explanation:

The distance between the other car and the intersection is,

x=x_{0}+V t \\ x=\frac{1}{2}+V t

The distance between the police car and the intersection is,

y=y_{0}+V t

y=\frac{1}{2}-40 t

(Negative sign indicates that he is moving towards the intersection)

Therefore the distance between them is given by,

z^{2}=x^{2}+y^{2}(\text { Using Phythogorous theorem })

z^{2}=\left(\frac{1}{2}+V t\right)^{2}+\left(\frac{1}{2}-40 t\right)^{2} \ldots \ldots \ldots(1)

The rate of change is,

2 z \frac{d z}{d t}=2\left(\frac{1}{2}+V t\right) V+2\left(\frac{1}{2}-40 t\right)(-40)

2 z \frac{d z}{d t}=V+2 V^{2} t-40+3200 t \ldots \ldots \ldots

Now finding z when t=0, from (1) we have

z^{2}=\left(\frac{1}{2}+V(0)\right)^{2}+\left(\frac{1}{2}-40(0)\right)^{2}

z^{2}=\frac{1}{4}+\frac{1}{4}=\frac{1}{2} \\ z=\sqrt{\frac{1}{2}} \approx 0.7071

The officer's radar gun indicates 25 mph pointed at the other car then, \frac{d z}{d t}=25 when t=0, from

From (2) we get

2(0.7071)(25)=V+2 V^{2}(0)-40+3200(0)

2(0.7071)(25)=V+2 V^{2}(0)-40

35.36=V-40

V=35.36+40=75.36

Hence the speed of the car is 75.36 mph

7 0
3 years ago
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