Question

particle of mass m and charge q is fastened to one end of a string fixed at point O. The whole system lies on a frictionless horizontal plane. Initially the mass is at rest at A a uniform electric field E is switched on in the direction shown in figure. The tension in the string when particle reach at point B is

Answer 1

Answer:

The work done by the tension of string is zero. Since there is no friction, only electric field does work.

qEl(1−cos60

∘

)=1/2mu

2

u=

qEl/m

At B, the tension in the string is responsible for centripetal acceleration,

T−qE=mv

2

/L=qE⇒T=2qE