Pitch is the sensation of certain frequencies to the ear. High frequency = high pitch, low frequency = low pitch.
f = c(speed of the wave) / <span>λ (wavelength)
1. 343m/s / 0.77955m = 439.99 Hz
This corresponds to pitch A
2. 343m/s / 0.52028m = 659.26 Hz
</span> This corresponds to pitch E
<span>
3. 343m/s / 0.65552m = 523.349 Hz
</span>This corresponds to pitch C
4. using f = c / λ
λ = c / f<span>
= 343m/s / 587.33 = 0.583999 m = 0.584 m
</span>
Average speed = total distance / total time
total distance = 40 + 20 = 60km
total time taken = 10 + 5 = 15 minutes
Average speed = 60/15 = 4km/min
For rotational equilibrium of the door we can say that torque due to weight of the door must be counter balanced by the torque of external force

here weight will act at mid point of door so its distance is half of the total distance where force is applied
here we know that

now we will have


so our applied force is 72.5 N
so the 1st on is the one on the left, middle is right and the 3rd one is the right one