A free proton and a free electron are placed in a uniform field. Which of the two
experience greater force and greater acceleration?

Let, E be the electric field in which an electron of mass m_e and a proton of mass m_p are placed. We know that force on a charge q placed in an electric field is given by, F = qE

The charge on the electron, q = -1.6 Х 10^-19 C

The charge on the proton, q = 1.6 Х 10^-19 C

Force on the electron, F_e = (-1.6 Х 10^-19)E = -1.6E Х 10^-19

Force on the proton is, F_p = (1.6 Х 10^-19)E = 1.6E Х 10^-19

Thus, the electron and the proton experience forces of same magnitude, but the forces are opposite in direction (negative sign in the force on electron suggests force on electron is directed opposite to the force on proton). Obviously, they will travel in opposite directions.

The magnitude on accelerations of electron and proton are dependent on their masses. The direction of acceleration of electron is opposite to the direction of acceleration of proton.

We have the relation between their accelerations and their masses.