A point source O is at the centre of a horizontal semicircular track of radius R. An infinite wall AB is tangent to the track. A block moves on the track with constant speed v from the point of tangency. If V and a are the speed and acceleration of its shadow on the wall, then:

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G1 Physics · Accepted Answer

If the angular position is φ=vt/R, the shadow coordinate on the tangent wall is y=R tanφ. Thus V=dy/dt=v sec²φ and a=dV/dt=(2v²/R)sec²φ tanφ. Hence B,D.