The Equation for the Change of Position of a Train $x = \frac { 1 } { 2 } a t ^ { 2 } + b t ^ { 3 }$

Multiple Choice

The equation for the change of position of a train starting at x = 0 m is given by $x = \frac { 1 } { 2 } a t ^ { 2 } + b t ^ { 3 }$ .The dimensions of b are

A) T ^{- 3}
B) LT ^{- 3}
C) LT ^{- 2}
D) LT ^{- 1}
E) L ^{- 1}T ^{- 1}