The question requires the use of kinematics and vector decomposition to calculate the horizontal displacement of a runner when she changes direction from the north to the east due to acceleration at a given angle.
The student is asking about the projection motion of a runner moving north, who accelerates at an angle. The question focuses on calculating the horizontal displacement (denoted as Δx) when the runner is running directly east. To solve this, one would have to break down the acceleration vector into its northward and eastward components and then use kinematic equations to determine the eastward displacement from the point of initial velocity to the point where the northward velocity component reaches zero and the runner is moving directly east.