The distance x covered by a body moving in a straight line in time t is given by the relation . If v is the velocity of the body at a certain instant of time, its acceleration will be
Differentiating with respect to t we have …….(i)
Now . Therefore, . Differentiating Eq. (i) with respect to time t, we have
where is the acceleration. But . Using this in Eq. (ii) we get . Hence the correct choice is (d).