6.If 1 kg of fuel is used in the above fusion reaction, the resulting helium has a mass of 0.993 kg. In other words, 0.007 kg of mass is converted to energy. How much energy is produced by
the fusion of 1 kg of hydrogen? (Hint: Use Einstein's equation, E = mc², where E is energy in
Joules, m is mass in kilograms, and c is the speed of light, 3 x 10 m/s.) (6 points)

answer and explanation;

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