An object moves in a straight line according to the equation x=2t ^ { 3 } -3t ^ { 2 } -6t where x is in meters and t is in seconds. At what time is the net Force acting on the object=0?​

A12-g wad of sticky clay is hurled horizontally at a 100-g wooden block initially at rest on a horizontal surface. the clay sticks to the block. after impact, the block slides 7.5 m before coming to rest. if the coefficient of friction between the block and the surface is 0.65, what was the speed of the clay immediately before the impact?