Question

A particle moving in a plane is acted upon by a force of constant magnitude. F and v denote instantaneous force and velocity of particle. F.v is zero at every moment of time. The path of particle is

(1) Straight line

(2) Circle

(3) Hyperbola

(4) Ellipse

Answer 1

(2) Circle

Since F.v = 0; the instantaneous velocity is always perpendicular to the instantaneous direction of force. This condition is satisfied for a particle moving in a horizontal circle with uniform speed. The force acting on particle provides the ncessary centeripetal force.