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Zielflug [23.3K]
3 years ago
7

Physical Science Pre-Test 2020-2021 Question: 1-10 The distance between Earth and the Moon was determined by measuring the time

it took for light waves from Earth to travel to the Moon and back. Why was it not possible to use sound waves for this experiment Sound waves must move through a substance Sound waves would change frequency on the return to Earth Sound waves move too slowly for the technique to be accurate Sound waves move more slowly in Earth's atmosphere than in space​
Physics
1 answer:
LiRa [457]3 years ago
5 0

Answer:

Option A - Sound waves must move through a substance

Explanation:

Unlike light waves, sound waves must travel through a medium/substance for such a medium to vibrate and then produce sound.

As a matter of fact sound can't travel through empty space.

Thus, looking at the options given, the correct one is:

Sound waves must move through a substance which is Option A

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Scenario
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Answer:

1) t = 23.26 s,  x = 8527 m, 2)   t = 97.145 s,  v₀ = 6.4 m / s

Explanation:

1) First Scenario.

After reading your extensive problem, we are going to solve it, for this exercise we must use the parabolic motion relationships. Let's carry out an analysis of the situation, for deliveries the planes fly horizontally and we assume that the wind speed is zero or very small.

Before starting, let's reduce the magnitudes to the SI system

         v₀ = 250 miles/h (5280 ft / 1 mile) (1h / 3600s) = 366.67 ft/s

         y = 2650 m

Let's start by looking for the time it takes for the load to reach the ground.

         y = y₀ + v_{oy} t - ½ g t²

in this case when it reaches the ground its height is zero and as the plane flies horizontally the vertical speed is zero

         0 = y₀ + 0 - ½ g t2

          t = \sqrt{ \frac{2y_o}{g} }

          t = √(2 2650/9.8)

          t = 23.26 s

this is the horizontal scrolling time

          x = v₀ t

          x = 366.67  23.26

          x = 8527 m

the speed at the point of arrival is

         v_y = v_{oy} - g t = 0 - gt

         v_y = - 9.8 23.26

         v_y = -227.95 m / s

Module and angle form

        v = \sqrt{v_x^2 + v_y^2}

         v = √(366.67² + 227.95²)

        v = 431.75 m / s

         θ = tan⁻¹ (v_y / vₓ)

         θ = tan⁻¹ (227.95 / 366.67)

         θ = - 31.97º

measured clockwise from x axis

We see that there must be a mechanism to reduce this speed and the merchandise is not damaged.

2) second scenario. A catapult located at the position x₀ = -400m y₀ = -50m with a launch angle of θ = 50º

we look for the components of speed

           cos θ = v₀ₓ / v₀

           sin θ = v_{oy} / v₀

            v₀ₓ = v₀ cos θ

            v_{oy} = v₀ sin θ

we look for the time for the arrival point that has coordinates x = 0, y = 0

            y = y₀ + v_{oy} t - ½ g t²

            0 = y₀ + vo sin θ t - ½ g t²

            0 = -50 + vo sin 50 t - ½ 9.8 t²

            x = x₀ + v₀ₓ t

            0 = x₀ + vo cos θ t

            0 = -400 + vo cos 50 t

podemos ver que tenemos un sistema de dos ecuación con dos incógnitas

          50 = 0,766 vo t – 4,9 t²

          400 =   0,643 vo t

resolved

          50 = 0,766 ( \frac{400}{0.643 \ t}) t – 4,9 t²

          50 = 476,52 t – 4,9 t²

          t² – 97,25 t + 10,2 = 0

we solve the quadratic equation

         t = [97.25 ± \sqrt{97.25^2 - 4 \ 10.2}] / 2

         t = 97.25 ±97.04] 2

         t₁ = 97.145 s

         t₂ = 0.1 s≈0

the correct time is t1 the other time is the time to the launch point,

         t = 97.145 s

let's find the initial velocity

         x = x₀ + v₀ cos 50 t

         0 = -400 + v₀ cos 50 97.145

         v₀ = 400 / 62.44

         v₀ = 6.4 m / s

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Answer: The correct answer is B. "the electromagnetic waves appear more red in color".

Explanation:

Scientists use the Doppler effect to understand the universe by determining the motion of the object.

Red shift: The apparent frequency of light decreases as the source object in space moves away from us.  The light is shifted to red end. The apparent frequency decreases and there is increase in the wavelength of the light.

Blue shift: The apparent frequency of light increases as the object in space moves towards us. The light is shifted to blue end. In this case, there is decrease in the wavelength of the light.  The frequency of the wave increases.

In the given problem, when the light source moves further away from an observer, the electromagnetic waves appear red in color.

Therefore, the correct option is (B).

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