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Question

# A mass m=20 g has a charge q=3.0 mC. It moves with a velocity of 20 m/s and enters a region of electric field of 80 N/C in the same direction as the velocity of the mass. The velocity of the mass after 3 sec in this region is–

A
80 m/s
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B
56 m/s
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C
44 m/s
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D
40 m/s
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Solution

## The correct option is B 56 m/sGiven:- m=20 g=20×10−3 kg q=3 mC=3×10−3 C E=80 N/C u=20 m/s In an electrostatic equilibrium, Electric force =ma So, qE=ma or, a=qEm=12 m/s2 From first equation of the motion we get, v=u+at =20+12×3 =56 m/s

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