We'll use the law of conservation of energy:

$\overline{){\mathbf{P}}{\mathbf{.}}{{\mathbf{E}}}_{{\mathbf{i}}}{\mathbf{+}}{\mathbf{K}}{\mathbf{.}}{{\mathbf{E}}}_{{\mathbf{i}}}{\mathbf{=}}{\mathbf{P}}{\mathbf{.}}{{\mathbf{E}}}_{{\mathbf{f}}}{\mathbf{+}}{\mathbf{K}}{\mathbf{.}}{{\mathbf{E}}}_{{\mathbf{f}}}}$

The work done by a proton is given by:

$\begin{array}{rcl}\mathbf{W}& \mathbf{=}& \mathbf{q}\mathbf{V}\\ & \mathbf{=}& \mathbf{(}\mathbf{1}\mathbf{.}\mathbf{602}\mathbf{\times}{\mathbf{10}}^{\mathbf{-}\mathbf{19}}\mathbf{)}\mathbf{[}\mathbf{30}\mathbf{-}\mathbf{(}\mathbf{-}\mathbf{10}\mathbf{\left)}\mathbf{\right]}\end{array}$

W = 6.408 × 10^{-18} J

A proton's speed as it passes point A is 50000 m/s . It follows the trajectory shown in the figure.(Figure 1)

What is the proton's speed at point B?

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