Aproton is released from rest at the positive plate of a parallel-plate capacitor. it crosses the capacitor and reaches the negative plate with a speed of 55000m/s . what will be the final speed of an electron released from rest at the negative plate?

You know the charge of a proton (the elementary charge in this case), you know its mass, and you know it's velocity. From there you can find its kinetic energy and from there you can find it's voltage. Once you know the potential difference there all you have to do is reverse the process. Multiply the charge of an electron by V and then solve for the velocity using the mass of the electron

a sonic boom is a loud boom that breaks the sound barrier

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