Two large parallel copper plates are 508 cm apart and have a

Two large parallel copper plates are 5.08 cm apart and have a uniform electric field of magnitude E = 6.95 N/C between them (see the figure). An electron is released from the negative plate at the same time that a proton is released from the positive plate. Neglect the force of the particles on each other and find their distance from the positive plate when they pass each other.

the tolerance is +/-1 in the 3rd significant digit

Solution

Force on proton and electron due to electric field is qE

Distance moved by the electron and proton in a time t is

    d_p = (1/2) ( qE / m_p ) t²

    d_e = ( 1/2) ( qE / m_e ) t²

When they cross each other, the times have to be equal . so

d_p m_p = d_e m_e

       d_p = (5.08 x10^-2 m) (9.11x10^-31 kg ) / ( 1.67x10^-27 kg)

              =27.71 x10^-6 m