Question

A particle of charge q = 4 mC and mass m = 10 mg starts moving from the origin under the action of an electric field and magnetic field . Its velocity at

(x, 3, 0) is . The value of x is –

• A.
• B.
• C.
• D.

Answer 1

Answer: (B)

Answer 2

W (qE) = + – 0

Ž4 × 10^–6 × 4x = $\frac { 1 } { 2 }$m (4²+ 3²) 4 × 10^–6 × 4 × x

= $\frac { 1 } { 2 }$× 10 × 10^–6 × 25 x

= $\frac { 250 } { 32 } \mathrm {~m}$ =