False because anti-lock brake system will activate automatically.
True - Because a sound wave carries energy; to propagate energy, energy must be applied for the sound wave to carry energy.
Answer:
-0.4D(maybe)
Explanation:
combined focal length (f)= 0.4m
D1 = 5D
Then f1= 1/D1
= 1/5 = 0.2 m
1/f=1/f1+1/f2
1/0.4=1/0.2+1/f2
f2= -5/2
D2=1/f2= -0.4D
Answer: Δβ (dB) = -13.1dB
Explanation:
The intensity of sound is inversely proportional to the square of the distance between them.
I ∝ 1/r²
I₁/I₂= r₂²/r₁² .....1
When the listener increases his distance from the source by a factor of 4.49.
Then,
r₂/r₁= 4.49
From equation 1
I₁/I₂ = (4.49)²
I₁/I₂ = 20.16
I₂/I₁ = 1/20.16
The change in sound intensity in dB can be given as
Δβ (dB) = 10 log(I₂/l₁) = 10log(1/20.6) = -13.1dB
Friction can be created to help you when you make a fire by rubbing two stones against each other to make a spark.
It can also be used as a problem when you want to push a big box across a rough or a gravel driveway. The friction slows the box down.
Hope this helps.