An electron is accelerated from rest through a ... - WAEC Physics 1998 Question

An electron is accelerated from rest through a potential difference of 70kV in a vacuum. Calculate the maximum speed acquired by the electron (electronic charge = -1.6 x 10^-19; mass of an electron = 9.1 x 10^-31kg)

3.00 x 10⁸ms^-1

2.46 x 10⁸ms^-1

1.57 x 10⁸ms^-1

1.32 x 10⁸ms^-1

correct option: c

ev = (\frac{1}{2})mv²

v² = (\frac{ev}{\frac{1}{2}m})

V = (\sqrt{\frac{ev}{\frac{1}{2m}}} = \sqrt{\frac{1.6 \times 10^{-19} \times 70 \times 10^3}{\frac{1}{2} \times 9.1 \times 10^{-31}}})

= (\sqrt{246.2 \times 10^{14}}) = 1.57 x 10⁸

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