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 -Suppose the physical characteristics of the crash test dummy accurately represent those of a human. What is the expected injury of the impact shown in Figure 2 if the head accelerated to 10 m/s at the end of the impact?

Question

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11ecba2d_12d2_00ec_a3bf_339e83dd62d6_MD0008_00 According to the passage, the type of injury can be determined from the collision duration and the average acceleration of the head during the collision. The average acceleration (a) of an object is its change in velocity (Δv) over the time (t) the object is accelerated: 11ecba2d_12d2_27fd_a3bf_2bc9d4c7e3e5_MD0008_00 According to the question, the head accelerated from a stationary position to a velocity of 10 m/s (Δv = 10 m/s), and the collision in Figure 2 lasted for 10 ms (t = 10 ms). This value is converted from milliseconds (ms) to seconds (s) using the conversion 1 s = 1,000 ms: 11ecba2d_12d2_27fe_a3bf_55d99aa1fba0_MD0008_00 Using these values, the average acceleration of the head was 11ecba2d_12d2_27ff_a3bf_4fb04c5fcf94_MD0008_00 In Figure 1, the point that represents an average acceleration of 1,000 m/s² for a duration of 10 ms lies above the threshold for a closed TBI but below the threshold for an open TBI (Choices A and C). Therefore, a closed TBI is expected, which is described in the passage as a brain injury that occurs without a skull fracture (Choice D). Educational objective: The average acceleration of an object is calculated as its change in velocity divided by the duration of the acceleration (a = Δv/t).

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