A U-shaped wire of mass 10 g and horizontal length 20 cm is in a uniform field B=0.1 T. A short current pulse transfers charge q=∫i dt, causing the wire to jump to height h=3 m. If q=√α coulomb, find α. Take g=10 m/s².

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G1 Physics · Accepted Answer

Magnetic impulse is ∫Fdt=Bℓ∫i dt=Bℓq=mv. The launch speed needed for height h is v=√(2gh). Hence q=m√(2gh)/(Bℓ)=0.01√60/(0.1×0.2)=√15 C. Therefore α=15.