A stationary motion detector sends sound waves of 0.225 MHz toward a truck approaching at a speed of 33.0 m/s. The speed of sound in the air is 343 m/s. What is the frequency of the waves reflected back to the detector

0.273 MHz

Explanation:

The frequency f₁ of the reflected waves to the stationary detector is given by

f₁ = f(v + v₁)/(v - v₂) where f = frequency of sound waves = 0.225 MHz, v = speed of sound in air = 343 m/s, v₁ = speed of detector = speed of truck = 33.0 m/s and v₂= speed of source of reflected wave = speed of truck = 33.0 m/s

f₁ = f(v + v₁)/(v - v₂)

  = 0.225MHz(343 m/s + 33 m/s)/(343 m/s - 33 m/s)

  = 0.225MHz × 376/310

  = 0.273 MHz

the working equation for the angular size is the product of the physical size and 360 degrees divided by the product of two pi and distance from earth. the minimum size would be 0.559 degrees while the maximum size would be 0.49 degrees. 

3. dark matter

empty space could also be a simple vacuum