de Broglie wavelength of accelerated electron

2018 1 question

1. An electron of mass m with an initial velocity $\vec{V} = V_0\hat{i}\ (V_0 > 0)$ enters an electric field $\vec{E} = -E_0\hat{i}$ ($E_0$ = constant > 0) at t = 0. If $\lambda_0$ is its de-Broglie wavelength initially, then its de-Broglie wavelength at time t is