A car speeding down a 20 foot hill
Answer:
B.) by interfering with sound waves
Explanation:
As we know that the interference of sound waves is of two types
1). constructive interference
2). destructive interference
now we know that constructive interference means the resultant intensity will be more than the intensity of interfering waves as here two waves are in same phase.
In destructive interference the resultant of two waves is given by the minimum resultant of the intensity as here the phase of two waves are opposite to each other.
So we will say that

here in case of noise cancelling headphones we know that the phase of noise is always made in opposite phase with the sound which is used to cancelled the noise.
This will reduce the noise and we will get a clear sound
C because mass is how much space an object takes up
The answer is C) A girl hangs by both hands, motionless, from a trapeze.
Answer:
75 Newtons.
Explanation:
From Newton's second law of motion,
F = m(v-u)/t................... Equation 1
Where F = force exerted by the ball on the bat, m = mass of the ball, v = final velocity of the ball, u = initial velocity of the ball, t = time
Given: m = 0.6 kilogram, u = 0 meter per seconds (at rest), v = 25 meters per seconds, t = 0.2 seconds.
Substitute into equation 1
F = 0.6(25-0)/0.2
F = 3(25)
F = 75 Newton.
Hence the magnitude of the average force exerted by the ball on the bat = 75 Newtons.