A particle of mass m and charge q has initial velocity v⃗=v₀ĵ. Electric field E⃗=E₀î and magnetic field B⃗=B₀î act on it. Its speed becomes twice the initial speed after what time?
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A particle of mass m and charge q has initial velocity v⃗=v₀ĵ. Electric field E⃗=E₀î and magnetic field B⃗=B₀î act on it. Its speed becomes twice the initial speed after what time?

G1 Physics · Accepted Answer

Magnetic force does no work. The electric field along x produces vₓ=(qE₀/m)t, while the initial perpendicular speed v₀ retains its magnitude. For total speed 2v₀: 4v₀²=v₀²+(qE₀t/m)², so t=√3mv₀/(qE₀). Hence C.