A particle is moving along x-axis with its position ($ x $) varying with time ($ t $) as: $ x = \alpha t^4 + \beta t^2 + \gamma t + \delta. $ The ratio of its initial velocity to its initial acceleration, respectively, is:
A particle is moving in a straight line. The variation of position $ x $ as a function of time $ t $ is given as: $ x = t^3 - 6t^2 + 20t + 15 $. The velocity of the body when its acceleration becomes zero is: