Question

A proton and an electron are released infinite distance apart and are attracted towards each other. Which of the following statement about their kinetic energy is true ?

• A. Kinetic energy of electron is more than that of proton
• B. Kinetic energy of electron is less than that of proton
• C. Kinetic energy of electron = kinetic energy of proton
• D. None of the above is true as it depends on the distance between the particles

Answer 1

Answer: (A)

Both particles move towards each other with equal and opposite forces.
Kinetic energy acquired, $K = \frac{1}{2} m v^2 = \frac{1}{2} m (at)^2 = \frac{1}{2} m \left( \frac{F}{m}t\right)^2$
or $K \propto \frac{1}{m}$