A small ball can move in a vertical plane along a semi–circle of radius r without friction. At what speed is the ball to launch from point A so that its acceleration is 3g at point B ?

Question

G1 Physics · Accepted Answer

At point B the tangential and normal components combine to give acceleration magnitude 3g. Using energy from A to B and the radial relation at B yields the launch speed v(A)=√(gr). Hence option C.