Answer:
Pr abs = (101.3+9.806*27.5) = 371 kPa (kN/m^2) .. or 3.71*10^5 Pa
F = Pr abs*A = 371 kN/m^2*(0.7854*0.35^3 m^2) = 35.7 kN..or 3.57*10^4 N
Explanation:
The change in frequency is called the Doppler effect. The speed of the car can be calculated by the formula for the Doppler effect for when the observer is standing still and the source of the sound is moving towards him:
f¹={V/(V-Vs)}*f,
where f¹ is the frequency of the car while moving towards the observer, V=343 m/s is the speed of sound, Vs is the speed of the car and f is the frequency of the car while standing still.
We need to solve the equation for the Vs:
f¹/f=V/(V-Vs)
V-Vs=V/(f/f¹)
-Vs=V/(f/f¹)-V
Vs=-V/(f/f¹)+V= -343/(300/330)+343=-343*0.91+343=-312.1+343=30.9 m/s
So the speed of the moving police car is Vs=30.9 m/s.
Answer:
This is an incomplete question. The complete question is --
An individual white LED (light-emitting diode) has an efficiency of 20% and uses 1.0 W of electric power.
How many LEDs must be combined into one light source to give a total of 3.8W of visible-light output (comparable to the light output of a 100W incandescent bulb)?
And the answer is --
19 LEDs
Explanation:
The full form of LED is Light emitting diode.
It is given that the efficiency of the LED bulb is 20 %
1 LED uses power = 1 W
So the output power of 1 LED = 0.2 W
We need to find the power required to give a 3.8 W light.
Power required for 3.8 W = Number of LEDs required = (total required power / power required for 1 LED )
= 3.8 / 0.2
= 19
Therefore, the number of LEDs required is 19.