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Question: A mass \(m = 20g\) has a charge\(q = 3.0mC\). It moves with a velocity of \(20m/s\) and enters a reg...

A mass m=20gm = 20g has a chargeq=3.0mCq = 3.0mC. It moves with a velocity of 20m/s20m/s and enters a region of electric field of 80N/C80N/Cin the same direction as the velocity of the mass. The velocity of the mass after 3 seconds in this region is

A

80m/s80m/s

B

56m/s56m/s

C

44m/s44m/s

D

40m/s40m/s

Answer

56m/s56m/s

Explanation

Solution

a=QEm=3×10−3×8020×10−3=12m/sec2a = \frac{QE}{m} = \frac{3 \times 10^{- 3} \times 80}{20 \times 10^{- 3}} = 12m/sec^{2}

Hence v = u + at ⇒ v = 20 + 12 × 3 = 56 m/s.