In a TV picture tube electrons are ejected from the cathode with negligible speed and reach a velocity of $5 \times 10^{6} \mathrm{~m} / \mathrm{s}$ in travelling one centimeter. Assuming straight line motion, find the constant force exerted on the electron. The mass of the electron is $9.1 \times 10^{-31} \mathrm{~kg}$.
$u=0$ (negligible)
$v=5 \times 10^{6} \mathrm{~m} / \mathrm{s}$
$v^{2}=u^{2}+2 a s$
$\left(5 \times 10^{6}\right)^{2}=(0)^{2}+2 a\left(1 \times 10^{-2}\right)$
$a=12.5 \times 10^{14} \mathrm{~m} / \mathrm{s}^{2}$
$F=m a=9.1 \times 10^{-31} \times 12.5 \times 10^{14}$
$=1.138 \times 10^{15} \mathrm{~N}$
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