A person with a black belt in taekwondo has a foot with a mass of 0.90 kg. Starting from rest, this foot attains a velocity of 8.3 m/s in 0.13 s. What is the magnitude of the average net force applied to the foot to obtain that acceleration?

57.42 N

Explanation:

We first find the acceleration knowing that it goes from rest to 8.3 m/s in 0.13 seconds,

Therefore, the acceleration is:

Now we use this to calculate the average net force by multiplying mass times acceleration:

F = m * a = 0.9 (63.8) = 57.42 N

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me