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## Homework Statement

## Homework Equations

W = -U for conservative forces

F = qV x B = qvBsinθ

W = Fd for conservative forces

K = 1/2mv^2

sinθ = 1 for 90° angles

E1 = E2 (conservation of mechanical energy)

## The Attempt at a Solution

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W = -U

-Fd = U

E1 = E2

K = U

K = -Fd = -qvBsinθd

K =-qvBd

-K/qd = Bv (1)

K = (1/2)mv^2

∴ v = sqrt(2K/m)

Substitute into (1)

-K/qd = B ⋅ sqrt(2K/m)

K^2/q^2d^2 = B^2 ⋅ (2K/m)

mK/2q^2d^2 = B^2

B = sqrt(mk/2q^2d^2)

Why is two in the denominator rather than in the numerator? Is my method invalid? If so, where can I improve? Thanks in advance.