The students notation and algebra is correct but the final answer is incorrect identify what is wrong with the problem and why is it wrong and correct it

A proton is launched with an initial velocity . from the negative plate of a parallel plate capacitor, as shown in the diagram below. The positive and negative plates of the capacitor are separated by a vertical distance d: the positive plate has a charge density of +Q/A, where A is the area of the plate and the negative plate has a charge density of -Q/A. A student is asked to determine the acceleration of the proton as it travels between the plates; their work is shown next to and below the diagram. They use q for the charge of the proton and Q for the charge on the plates. EF = ma = _ Fu = may + + + + + + + + Q /A KQq -qEy + ( d - r) 2 = may + - Q/A KQ k Qq - 9 72 + ( d - r ) 2 = may kQq kqQ + ay = m ( d - r ) ? md2 kqQ ay (d - r) 2