A planet of mass M and radius R has no atmosphere. The escape velocity at its surface is ve. An object of mass m is at rest a distance r from the center of the planet, where r>>R. The particle falls to the surface of the planet. The total mechanical energy of the particle at the surface of the planet is closest to

Explanation:

Expression for escape velocity

ve =

ve² R / 2 = GM

M is mass of the planet , R is radius of the planet .

At distance r >> R , potential energy of object

=

Since the object is at rest at that point , kinetic energy  will be zero .

Total mechanical energy  = + 0 =

Putting the value of GM = ve² R / 2

Total mechanical energy  = ve² Rm / 2 r

This mechanical energy will be conserved while falling down on the earth due to law of conservation of mechanical energy  . So at surface of the earth , total mechanical energy

=  ve² Rm / 2 r

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