Question

the bob of a simple pendulum has a mass of 60g and a positive charge of 6 x 10-6 c.

Answer 1

m = 40 g, q = 4 × 10–6 C Time for 20 oscillations = 45 sec. Time for 1 oscillation =45/20 sec

Answer 2

charge on bob, C = 4.0 micro coulumb

electric field, E = 2.5 x 104 N/C

thus force on the bob, F = CE = 0.1 N

mass of bob, m = 40g = 0.04 kg

thus external acceleration on bob = F/m = 2.5 m/s2

thus nt acceleration of bob in downward direction, A = g-a = 9.8 - 2.5 = 7.3 m/s2

let lenght of pendulum = L

initial time period = 45/20 = 2pisqrt(L/g)

thus we can find L

and hence the new time period

and thus time taken for 20 oscillations