Particle P starts from the origin and moves along the circular path shown. Particle Q crosses the x-axis when P leaves the origin and moves with constant speed v parallel to the y-axis, always having the same y-coordinate as P. When P reaches the diametrically opposite point B, its average speed is:

Question

G1 Physics · Accepted Answer

When P goes from O to the diametrically opposite point B, it travels a semicircular distance πR. Q must move vertically through the diameter 2R with speed v, so the common time is 2R/v. Average speed of P =πR/(2R/v)=πv/2. Hence option B.