Passage A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force. In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site. This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI. If there is no skull fracture, the injury is classified as a closed TBI. The type of TBI can be predicted from the collision duration and the average acceleration of the head. The thresholds for open and closed TBI are shown in Figure 1. Figure 1 Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes. The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity. The linear acceleration of the crash test dummy's head was recorded during and after the impact. The results for a trial in which the impact lasted for 10 ms are shown in Figure 2. Figure 2 The acceleration of the head during and after a 10-ms collision -If a baseball traveling at 20 m/s strikes a player running at 5 m/s, what is the difference between the minimum and maximum possible relative velocities between the ball and the player?

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11ecba2d_12d2_7620_a3bf_2ba04f695c5c_MD0008_00 The relative velocity of the ball with respect to the player is the apparent velocity of the ball from the player's perspective (also known as its frame of reference), or vice versa. Velocity is an example of a vector, which is a quantity that includes magnitude (eg, speed) and direction (eg, east). Therefore, the relative velocity between two objects depends on their relative directions. The minimum relative velocity occurs when the ball and player are moving in the same direction. The relative velocity is their difference (vector subtraction): v = 20 m/s − 5 m/s = 15 m/s The maximum relative velocity occurs when the ball and the player are moving in opposite directions. The relative velocity is their sum (vector addition): v = 20 m/s + 5 m/s = 25 m/s The difference between the minimum (15 m/s) and maximum (25 m/s) possible values is 10 m/s. (Choices B and D) The minimum and maximum possible values are 15 m/s and 25 m/s, respectively. Educational objective: The relative velocity between two objects depends on their directions. The minimum relative velocity occurs when the velocities are the same direction, and it is determined by vector subtraction. The maximum relative velocity occurs when the vectors are pointed in opposite directions, and it is determined by vector addition.

Passage A Traumatic Brain Injury (TBI) Is a Form of Brain